In the electricity market, electric vehicle charging stations can reduce the cost of electricity by optimizing bidding strategies. Based on the flexible load-storage characteristics of electric vehicles, this paper proposes a secondary bidding strategy for electric vehicle charging stations in the day-ahead market. Firstly, the Minkowski summation method is used to establish an EV cluster model, and the EV charging station is regarded as a generalized virtual energy storage device to evaluate its dispatchable capacity in today’s market. Then, a secondary bidding strategy based on joint bidding is proposed for electric vehicle charging stations to participate in the day-ahead market, in which the optimal decision-making of charging stations forms the upper layer and market clearing constitutes the lower layer, constructing a multi-objective double-layer planning bidding model. Finally, in the case study analysis, the results indicate that the Minkowski summation method effectively reduces the complexity of the model while maintaining the constraint relationships between variables. Additionally, the secondary bidding strategy for the charging station day-ahead market based on joint bidding can effectively reduce the power cost of the charging station when participating in the day-ahead electricity market.