Opportunity co-creation is the prerequisite for start-ups to promote entrepreneurship development and maintain competitive advantage under the influence of entrepreneurial platform empowerment. Based on the perspective of affordance theory, this paper constructs the two stages process model of realizing opportunity co-creation between entrepreneurial platform and start-ups through a longitudinal case study of the entrepreneurship interactive practices of HCH Ventures and Xiaoshuai Theater Technology from 2015 to 2023, which represent core actors in the entrepreneurial ecosystem. The study reveals the process mechanism of entrepreneurial platform affordance actualization to promote opportunity co-creation. The case study found that in the context of entrepreneurial ecosystem: (1) The interaction between the functions of the entrepreneurial platform and the goals of start-ups generates multiple action possibilities, including entrepreneurial initiation, fitting-in, stabilization and pivot affordances. (2) The diverse entrepreneurial activities conducted by start-ups based on the four types of entrepreneurial platform affordances constitute the key process elements for the realization of affordances and serve as the core link connecting affordances to opportunity co-creation. (3) Under the role of different entrepreneurial activities, start-ups complete the transition from emergence to sustainable development, and gradually reach the goal of opportunity co-creation with entrepreneurial platform. The research findings hold significant theoretical and practical value for understanding the synergistic interactions between entrepreneurial platforms and new ventures within the entrepreneurial ecosystem context.