The electrolyzer is a key equipment in renewable energy electrolysis hydrogen technology, and its performance directly affects the efficiency, stability, and cost of hydrogen production. An optimization method for the capacity configuration of mixed electrolysis cells in wind solar hydrogen storage systems based on flexibility indicators is proposed. Firstly, a flexibility evaluation index system is constructed from four perspectives：fluctuation adaptability, hydrogen production efficiency, operating conditions, and economy, to comprehensively evaluate the comprehensive performance of electrolysis cells under various operating conditions. Secondly, combining the AHP-DEMATEL method to determine the weight allocation. Finally, the flexibility index is embedded into the optimization framework to conduct research on the configuration strategy of the hybrid hydrogen production system. The simulation results show that the hybrid electrolyzer capacity optimization configuration scheme proposed in this paper is significantly lower in hydrogen production cost than the single electrolyzer configuration scheme, correspondingly higher in hydrogen production volume than the single alkaline electrolyzer scheme, and provides a new method for the selection and evaluation of hybrid electrolyzers.