Abstract: The innovation activities of enterprises are gradually from closed to open, and the On-line User Innovation Communities(Abbreviation OUIC) has become an important place for enterprise innovation. On-line User Innovation Communities such as Dell′s "Idea Srorm", Xiaomi′s "MIUI" and Haier′s "HOPE" platform have brought a large number of users into the innovation system in an efficient and low-cost way, and achieved remarkable innovation results. The On-line User Innovation Communities based on Internet collaboration refers to the online community operated by enterprises with product R & D and improvement as the goal and community members as the source of innovation. At present, it has become an important platform for enterprises to attract users to participate in product R&D innovation and a typical model of open innovation. User participation in On-line User Innovation Communities knowledge creation will not only affect the product innovation performance of enterprises, but also affect the core competitiveness of enterprises in the market. However, On-line User Innovation Communities has the characteristics of anonymity,uninterrupted, not facing each other and non constraints, and relatively few members are able and motivated to participate in community innovation. Therefore, it is not easy for enterprises to obtain rich and valuable information such as product user experience, improvement suggestions and new creative ideas through operation OUIC. According to Yan Jianyuan et al studies, among the more than 1000 enterprises that have established On-line User Innovation Communities,more than half fail to get the expected economic benefits and returns. Therefore, in order to successfully attract and motivate users continuous participation in product innovation, it is necessary to profound understanding the influencing factors of users′ participation in On-line User Innovation Communities co creation value. In recent years, researches on On-line User Innovation Communities mainly focus on innovation motivation, user motivation, innovation performance and innovation management, among which motivation is one of the most important research perspectives. However, the traditional research on Innovation participation motivation still has the following shortcomings: First, although based on the theory of organizational behavior, both internal and external motivation can promote the creation of user innovation behavior, there are some problems, such as the internal motivation of users does not fully in accordance with the organizational goals, and the external motivation keeps upgrading, which leads to ineffective motivating et al. Secondly, unlike open source community, brand community and social community, On-line User Innovation Communities has two attributes: user participation in innovation and online social interaction. Therefore, it is necessary to study the motivation factors, mechanism and effect of user innovation behavior from a new theoretical perspective; Third, Benabou pointed out that according to the theory of social embeddedness, doing what you like, external reward and impression management are important factors of individual economic behavior. In summary, in addition to internal and external motivation, impression management which the psychological tendency that people want to be viewed positively and avoid being viewed negatively by others, which becomes an important motivation for users to participate in On-line User Innovation Communities innovation. However, throughout the existing literature, scholars mostly study the internal and external motivation from the perspective of user innovation or enterprise innovation, and few scholars study the two attributes of On-line User Innovation Communities from the perspective of impression management. Therefore, based on the perspective of social psychology, taking on-line impression management as the core concept, this paper studies the User Innovation participation motivation, impression construction behavior and the impact on innovation performance. Research findings: (1) To community members pursuing knowledge co creation motivation and network social intercourse motivation,the probability of adopting Acquired Impression Management is significantly higher than that of adopting Defensive Impression Management; To Community members pursuing community identity motivation,the probability of adopting Defensive Impression Management behavior is significantly higher than that of adopting Acquired Impression Management behavior. The findings provide theoretical guidance and practical enlightenment for enterprises to effectively motivate and classify management users in On-line User Innovation Communities. (2) The longer the community age the members of On-line User Innovation Communities are, the stronger the Defensive Impression Management behavior is; The shorter the community age the members of On-line User Innovation Communities are, the stronger the acquired impression management behavior is. The traditional view is that "senior people" are more experienced and capable, However, this study shows that in On-line User Innovation Communities with social attributes, "job burnout", "sophisticate" and so on all are the important manifestations of "senior people" positive not as good as "junior people". This provides theoretical support and policy enlightenment for the enterprise to carry out "turfing the old and absorbing the new" in the On-line User Innovation Communities. Compared with the defensive impression management, the acquired impression management has a more positive impact on the innovation performance of the On-line User Innovation Communities. Enterprises can encourage users to adopt acquired impression management behavior, actively participate in innovation, and at the same time create an inclusive community atmosphere, reduce defensive impression management behavior, so as to improve community innovation performance. The theoretical significance of this study is to expand the research vision of impression management and online user innovation community and enrich the open innovation theoretical system; First, for impression management, an important organizational phenomenon, scholars explore innovation from the perspective of organizational citizenship behavior, suggestions behavior and face. This study introduces the impression management theory framework to study the user innovation participation behavior and effect of online user innovation community, expands the research vision of impression management and online user innovation society, and lays a foundation for further using the theory to explore open innovation. Second, this study is different from the previous perspective based on the incentive theory of organizational behavior, such as internal motivation and external motivation, From the perspective of social psychology impression management, this paper constructs a theoretical model to explain the influence of user′s participation motivation in innovation, that is, the pursuit of knowledge co creation, the pursuit of online social intercourse and the pursuit of community identity on users′ participation in innovation. Furthermore, it reveals the different working mechanism of acquired impression management and defensive impression management, explains the necessity of distinguishing acquired impression management and defensive impression management in research and management, and enriches the theoretical system of user innovation behavior. Third, it is different from previous studies that regard personal characteristics such as online community age and other factors as insignificant control factors, This study has a keen insight into the social attributes of online user innovation community. Based on the inspiration of "strong relationship" and "weak relationship" of sociology, it introduces the regulatory variable of community age, which has typical social attributes, to build a research model, and verifies the regulatory role of social age on two types of impression management behaviors, which further enriches the impression management theory system. The significance of management practice is to provide management suggestions for enterprises to identify different users′ participation motivation and formulate effective incentive strategies, so as to improve innovation performance.

Key words: on-line user innovation communities, product development innovation, community identity, online impression management, innovation performance