Abstract: Based on institutional theory, this paper utilizes enterprises in Tianfu Software Park in Chengdu as the empirical example, proposes and validates that by being isomorphic, enterprises can gain cognitive legitimacy from open source communities, and further develop collaborative innovation networks that are tightly coupled. Specifically, this paper portrays the process of isomorphism from two dimensions - institutional and behavioral, respectively. The former focuses on governance mechanism, while the latter points to business model. The regression results show that both two paths of isomorphism are positively related to the degree of coupling of enterprises and open source communities, and the relationship is mediated by cognitive legitimacy. The findings not only provide a feasible way for commercial organizations to better integrate into open innovation platforms represented by open source communities, but also supplement and extend institutional theory by decomposing the process of isomorphism into two dimensions. This paper also contributes by breaking the presupposition that the targets with which to be isomorphic should be limited to organizations with the same nature.