The large-scale energy storage with fast,accurate and instantaneous throughput capability undertakes automatic generation control to provide a high-quality resource for secondary frequency regulation in each control area. In order to allocate a reasonable-scale energy storage resource to the application scenarios of different power structure features, a storage capacity allocation method using CPS index evaluation is proposed. First, for the two power supply structures based on thermal power and hydropower formed in China, a simulation model of thermal power and hydropower interconnection system is proposed. Then, on the basis of the analysis of the frequency regulation condition and the consideration of the power characteristics of the abundance and dry season, the frequency allocation instruction method for different working conditions is proposed. Finally, the degree of contribution of the quantified energy storage by simulation calculation verifies that the energy storage frequency modulation requirements of different scenes are different, and the performance extremes and economic extremes of the energy storage capacity configuration in different scenarios are obtained by using the CPS performance evaluation index and its improvement. The proposed model and research results have important guiding significance for rational planning of energy storage capacity in each control area.