Windows of opportunity refer to "the length of time for the development space of the market to exist", during which enterprises can enter new markets and realize profits and returns on investment. The opportunity window is created by the combination of one or more factors, such as technology paradigm shift, business cycle turnover or government policy regulation , which can be further divided into four dimensions: technology window, demand window, stakeholder window and policy window. It can be found that the opportunity window covers multi-level situational factors of demand, market and system, which provides an important theoretical basis for explaining the legalization of entrepreneurial enterprises under institutional flexibility. Organizational legitimacy refers to the consistency between the social values related to or represented by organizational activities and the accepted code of conduct of the social system , Weber was introduced from the field of political science to the field of sociology for the first time to discuss social order and norms, early research focused on governance legitimacy and political legitimacy, etc., Later, influenced by the theories of strategy, resource, innovation and entrepreneurship, the research scope has been extended to enterprises, non-profit organizations and other fields, the research content continually get rich and perfect. Legalization research based on the background of western mature market economy generally has two kinds of views: institutional view and strategic view. Scholars of the system view represented by Dimaggio focus on internal guidance, emphasizing the internalization of social regulation, norms and cognition, and believe that legitimacy, as an internal need of an enterprise, can be obtained through organizational isomorphism or organizational convergence. Scholars of strategic view represented by Elsbach lay emphasis on external guidance, emphasize the initiative role of enterprises, and believe that enterprises can build legitimacy by compliance, selection, manipulation, creation and other legalization strategies in response to institutional environment. Based on the interpretation of the local institutional context, it is believed that informal relationships such as strategic alliances, entrepreneurs′ social skills and relationship networks(especially political relations) are important driving factors for new enterprises to break the legal constraint. On the other hand, taking the legitimacy acquisition process in the internationalization of emerging economies as the research object, it points out that organizational resource liquidity is the micro basis for enterprises to choose legalization strategy, and further explains that complementary resources in transnational strategic alliances can help enterprises construct organizational legitimacy to cope with the "dual" institutional situation. It can be found that the existing research in the process of legitimacy for emphasizes the system factors, mapping to the domestic research is focus on strategic alliance and the important role of organizational resources, this article has provided the beneficial reference and revelation, but still there are a few points can continue to deepen the single institutional factors: (1) Flexible situation cannot fully explain the system or the system of Internet start-ups legalization of strategic actions, the chance factors need to consider the market situation, from the Angle of the window of opportunity to build a more complete analysis framework. (2) Existing studies focus on the relationship between organizational resources and legitimacy, ignoring the important role of different types of dynamic capabilities in the acquisition mechanism of organizational legitimacy, and cultivating and constantly improving the dynamic capability system is an important factor for entrepreneurial enterprises to break resource constraints and build competitive advantages. (3) The existing research focuses on the static point of view, the lack of analytical from the perspective of dynamic evolution mechanism of legitimacy for Internet start-ups, it studies have shown that legitimacy is not "once and for all" and "overnight" , so you need to complement ability elements, from the perspective of dynamic evolution update and upgrade the enterprise resource and ability, in order to better resolve the complex environment of the Internet start-ups to build strategic actions in the process of legal status.

Based on the above practical and theoretical background, this paper uses case study method to construct a theoretical framework of opportunity window, dynamic capability and legalization strategy evolution from the perspective of dynamic evolution, aiming to solve the following problems: What roles do opportunity window and dynamic capability play in the legitimacy acquisition of Internet start-ups? Study found that: (1) Organizational legitimacy construction path including "trigger-response-action" three links: the window of opportunity to trigger the enterprise dynamic ability to complete the strategic use of cognitive level focus, dynamic capacity and adaptive behavior level select legal strategy in response to the opportunity window, finally legalized by strategic guidance enterprise strategic action to achieve legitimacy. (2) The process of organization legalization is accompanied by constant transition from low-order dynamic capability combination to middle-order dynamic capability combination and then to higher-order dynamic capability combination. At the same time, the enterprise strategic action also presents the behavior characteristic from passive to active. The research results have made theoretical contributions to the research on the legitimacy of start-ups in the local context, and have enlightening significance for Internet start-ups to break through the legitimacy constraints of emerging industries.