The ecological development of digital platform has become an inevitable trend, but the academic research on digital platform ecology is still in its infancy. This study takes WeChat platform as the case study object, and adopts the longitudinal case study method to explore the allocation of border resources by core enterprises and the evolution of the relationship between core enterprises and complementors in the process of ecological evolution of digital platform. It is found that the dynamic allocation of boundary resources is the key factor in the ecological evolution of the platform, and the core enterprises promote the ecological evolution of the platform by designing and deploying boundary resources, adding and updating them, and reusing and redesigning them. Core enterprises connect different complementors at different stages of ecological development, including transactional complementors, innovative complementors and mixed complementors; The three types of complementary people build resource-based dependency relations with core enterprises. According to the endogeneity and exogeneity of resources, three types of dependency relations are obtained, namely structural dependency, process dependency and mixed dependency, and the dynamic changes of dependency degree are analyzed. Core enterprises should master the stage characteristics of ecological development and make use of the dynamic nature of border resources to realize the ecological development of the platform and the healthy maintenance of the relationship between complementors.