To address renewable energy output fluctuations and enhance power system flexibility, a multi-energy complementary system integrating wind power, photovoltaic generation, pumped storage hydropower and electrochemical energy storage is constructed. A month-level development scheduling method for pumped storage is proposed, which incorporates the development, construction and commissioning timing of pumped storage sites into the decision-making framework. By comprehensively considering annual investment limits, power load demand, wind-solar output fluctuations and storage capacity enhancement, a long-term, month-scale capacity allocation model for pumped storage stations is formulated. Results from a typical regional case study demonstrate that the proposed model achieves dynamic and fine-grained allocation of pumped storage capacity across different months, significantly improving resource utilization efficiency and reducing wind and solar curtailment.