Abstract: To reduce the difficulty for electric vehicle (EV) users to participate in the day-ahead frequency regulation ancillary services market and improve their participation enthusiasm, by introducing the net income of EV when charging off the grid and the impact of battery power on user psychology into the value function of prospect theory, a day-ahead decision model for EV users to participate in frequency regulation auxiliary service market under bounded rationality was established. This model considers the battery aging cost of EVs participating in frequency regulation auxiliary service, studies the optimization strategy of EV reserve capacity, and the quotation strategy of the frequency regulation auxiliary service market. In addition, three feasible simplified EV frequency regulation auxiliary service participation modes were provided for users to choose from. The effectiveness and feasibility of EV users' day ahead FM decision model based on prospect theory was verified through the analysis of a numerical example, and it is more consistent with the actual EV users' decision-making behavior.