Abstract:    In the context of transformation and upgrading, enterprises try to make transformation through innovation in products, processes or business models, but the success of innovation activities is relied on legitimacy. Innovation legitimacy indicates the degree of recognition and acceptance of innovation activities by external stakeholders under the constraints of social norms and other systems. Although the impact of knowledge or resource on innovation legitimacy has attracted much attention, the relevant researches about the effect of knowledge search on innovation legitimacy have been neglected, and the decision-making situation of this impact has not been revealed. Moreover, causal reasoning and effectual reasoning are complementary to each other, but the mechanism differences of the two decision-making rationalities and the integration effect between them need to be further explored. Integrating the theory of knowledge search, innovation legitimacy and decision rationality, this paper constructs the model of adaptive search and transformative search on innovation legitimacy, as well as the moderating models of causal reasoning and effectual reasoning. 
    This paper firstly defines and analyzes the relevant theories and concepts of knowledge search, innovation legitimacy and decision rationality based on the literature review. The conceptual model of knowledge search effects on innovation legitimacy is put forward based on theoretical discussion. Then, data of 212 manufacturing enterprises in Yangtze River Delta and Pearl River Delta are used to testify the research hypothesis with statistical methods, such as correlation analysis, reliability and validity analysis, and multilevel regression analysis. The results show that adaptive search has an inverted U-shaped effect on innovation legitimacy, while transformative search has a U-shaped effect on innovation legitimacy. Causal reasoning strengthens the relationship between adaptive search and innovation legitimacy, but weakens the relationship between transformative search and innovation legitimacy. However, effectual reasoning weakens the relationship between adaptive search and innovation legitimacy, but strengthens the relationship between transformative search and innovation legitimacy. Furthermore, the duality decision rationality of causal reasoning and effectual reasoning positively moderates the relationship between adaptive or transformative search and innovation legitimacy. 
    This research not only enriches the knowledge search and decision-making rationality, but also provides theoretical reference for manufacturing enterprises to obtain the innovation legitimacy and realize the transformation. Firstly, enterprises should balance the use of adaptive search and transformative search strategy to break through the "legitimacy threshold" of innovation at different stages of entering the market. Secondly, enterprises should pay more attention to the match of managers′ decision-making rationality and knowledge search strategy, so as to obtain innovation legitimacy. Finally, enterprises should use the duality decision rationality of causal reasoning and effectual reasoning to obtain diversified knowledge and avoid falling into the extreme situation of decision-making, so as to use different search strategies to enhance the support of stakeholders for innovation. 

Key words: knowledge search, innovation legitimacy, causal reasoning, effectual reasoning