To achieve the cooperative participation of electric vehicle (EV) in power network frequency control, it is necessary to allocate the frequency regulation power in the real-time phase. In view of these practical problems, this paper proposes a real-time power allocation method for EVs participating in frequency regulation service considering battery loss. Firstly, the EV parking time conversion method is proposed, and the feasible domain of EV is characterized by considering the discharge depth. Secondly, the power allocation model of EV fleet based on state conversion is proposed to reduce battery loss. Finally, the simulation results show that the proposed method can effectively reduce EV charge-discharge conversion times and ensure EV power demand. Compared with the traditional method, the response error of frequency regulation signal is reduced by about 90%.