The high-proportion new energy connected to the grid will aggravate the pressure of power system frequency regulation. Participation of energy storages such as lithium batteries and supercapacitors in frequency regulation can effectively improve the frequency regulation performance and increase the new energy accommodation. Starting from the unbalanced components of the power system such as the net load fluctuation and the forecast deviation, and considering the complementarity characteristics of the wind and photovoltaic power forecasting errors, based on the variational modal decomposition and Monte Carlo simulation, a method for measuring the frequency regulation capacity and rate demand of the power system is proposed. The probability distribution statistical modall and the frequency regulation cost-benefit modall are used to evaluate the demand for hybrid energy storage, and the relationship between the frequency regulation capacity of the power grid and the demand for hybrid energy storage under different new energy installed ratios is compared. A provincial power grid in China is taken as an example to verify the effectiveness of the proposed method.