With the integration of high-proportion renewable energy and the deepening of electricity market reform, solving the dif-ficult fixed cost recovery for traditional generators and en-suring system capacity adequacy have become critical issues. A phased capacity adequacy guarantee mechanism adapting to the deep transformation of the power structure is proposed, covering three evolutionary stages including fixed capacity compensation in the pilot phase, category-based competitive compensation in the transition phase, and a unified capacity market in the mature phase. First, a fixed capacity accounting method based on cross-market expected revenue is designed to guarantee the fixed cost recovery of initial baseline flexible power sources. Second, a category-based competitive com-pensation model is developed for heterogeneous resources with different regulation characteristics, guiding various flexible resources to participate in bidding independently. Finally, a centralized clearing mechanism for the unified capacity market is designed to coordinate long-term capacity investment decisions. Case study results show that the pro-posed phased capacity adequacy guarantee mechanism can ensure effective fixed-cost recovery for generation enter-prises, guide the reasonable investment in flexible resources such as energy storage, and thereby guarantee long-term system capacity adequacy and flexible regulation capability.