With the popularization of electric vehicles(EVs), it has become the focus of research to guide EVs in charging stations(CS) to participate in frequence control(FC). The premise of auxiliary FC of CS is to accurately evaluate the real-time dispatchable power of CS. Therefore, this paper proposes a real-time dispatchable power evaluation method based on user demand. First, the calculation method of FC participation factor considering the user demand and EVs’ real-time states of charge (SOCs) is proposed, and based on this, the classification method of EVs is proposed. Then, the regulation boundaries of real-time SOCs of EVs in different situations are explored, and based on this, the real-time dispatchable power evaluation method of CS is proposed. Finally, MATLAB/Simulink simulation is used to verify the feasibility of the classification method of EVs based on FC participation factor, and the simulation obtains the change of real-time dispatchable power of CS during the study period. The data can provide reference for the research work of power grid planning, CSs construction and vehicle-road-network interaction.