Abstract:    Aiming at the deficiencies in theoretical research and combining with the specific practice of enterprises, this paper discusses what needs to be studied at first. Based on the description of situational factors and open innovation types, this paper tries to extract the basic experience of open innovation implementation from commonness and difference through the comparison of P&G, Huawei and Haier, and discusses the following three problems in detail: (1) How to categorize and depict open innovation types intuitively? (2) Is there a general law in the evolution of the open innovation path of different enterprises? (3) Does each situational element affect the setting of open innovation model? What is the mechanism of the impact? 
    The method of case study is especially suitable for dynamic research, and can deeply analyze the internal mechanism of problem development. This paper studies the evolution law of open innovation in different open innovation situations, that is, to solve the problems of "when" and "how", so it is more suitable to use the method of case study to extract undiscovered conclusions from phenomena. And multi-case study is more suitable for the construction of dynamic process model, so this paper chooses the method of multi-case study.
   Following the design of multi-case study, the data analysis mainly consists of three key steps: firstly, the case enterprise data are preliminarily combed, narrative simplification and classification with the logic of "innovation situation" and "open innovation type"; secondly, the evolution process of open innovation type of each enterprise is combed with specific logic, and the results are discussed by replication and difference logic; finally, based on the principle of single variable, this paper discusses the influence of each element in the innovation situation on the open innovation type, analyzes the internal matching logic between the situation and the type.
   Based on the guidance of relevant data, the indicators mentioned in the existing literature are reorganized and classified by repeated comparisons and iterations between the case data, the construction relationship and the existing theories. Finally, this paper describes the specific characteristics of each stage of open innovation in two dimensions: open model and the nature of partners. The cooperation model is divided into four levels: the degree of cooperation close, the form of cooperation, the open node and the transaction logic, and the nature of partners are described from two aspects: their spatial distribution characteristics and the types. According to the stage characteristics of enterprise opening, marked by the transformation of the close degree of cooperation in open innovation, the stage of open innovation is divided into primary open stage, mature open stage and leading opening stage.
   In view of the research gap in the theory, taking the practice of Haier, P&G and Huawei as examples, this paper compares and iterates the case material orientation with the existing theoretical knowledge repeatedly, and tries to obtain the general law of the evolution of open innovation path and the internal mechanism of the effect of situation on open innovation, so as to provide some theoretical reference for the application of enterprises. The main results are as follows: (1) the definition of open innovation type can be described in two dimensions: open model and partner nature, among which, open model can be divided into four aspects: the degree of cooperation close, the form of cooperation, the open node and the transaction logic; and the nature of partner is mainly reflected in the spatial distribution and type of partner. These two dimensions depict the openness of the enterprise intuitively and quantitatively; (2) based on the degree of cooperation close, most of the open innovation of different enterprises goes through the "primary open stage-mature open stage-leading open stage". At the same time, the degree of cooperation close in these three stages is contractual, teamwork and strategic cooperation; (3) the internal situation of enterprises will affect the evolution of open innovation model. Among them, innovation strategy will affect three dimensions: the degree of cooperation close, the form of cooperation and the type of partnership; the type of partners changes with the change of organizational structure; the change of enterprise scale may affect the choice of cooperation form and spatial distribution of partners; (4) the external situation of enterprises is also an important influencing factor in the evolution of open innovation model. Among them, industry characteristics will affect choice of partner type, degree of close cooperation, spatial distribution and cooperation form of the organization; the form of cooperation, spatial distribution and partner type change with the change of industry situation; innovation environment will have an impact on partner type and transaction logic.
   The enlightenment of this conclusion to the practice of enterprises is that: (1) Open innovation is a gradual process, in which the open node is an important controllink, it should be limited to the level of non-core technology no matter in what stage of opening. (2) Both the perspective of dynamic capability and the perspective of resource-based view emphasize that open innovation can bring some advantages to enterprises, but the premise is that the open model must be set reasonably according to the situation. The empirical accumulation brought by open innovation constitutes the resource basis of the enterprise, and it is also the key to the formation of the core competence of the enterprise. (3) In open innovation, the influence of external situational factors (such as industry attributes, innovation environment, etc.) on the choice of open model of enterprises is greater than that of internal situations. Among them, the industry attribute and the industry potential have a great influence on the open model. (4) In the open innovation, the successful setting of the resource transit platform can reduce the search cost and improve the innovation efficiency. However, the key is to improve the resource attractiveness and resource flow rate of the resource transit platform. (5) Open innovation is an innovation mechanism to ensure that enterprises can obtain Schumpeter innovation rent and Ricardo scarce rent at the same time, but enterprises must pay attention to basic R&D in order to avoid the potential dependence brought by open innovation and ensure their own R&D strength. The above conclusions provide a certain theoretical reference for the setting of open model of enterprises.

Key words: open innovation, situation, multiple case