Abstract: With the integration of large-scale intermittent new energy, the safe and stable operation of the power grid faces great challenges. If the scheduling characteristics of electric vehicles (EVs) can be fully exploited, the operational flexibility of power grids will be significantly improved. The primary objective of this study is to provide ancillary services through the aggregation of electric vehicle charging stations (EVCSs) to participate in grid interaction, thereby ensuring the effective power balance and the safe and stable operation of the power grid. An efficient resource aggregation strategy for EV charging stations is proposed. Based on the charging demand of vehicle owners and EV charging characteristics, the feasible region of EV charging piles is accurately described, and an EVCS equivalent battery (EVB) model is developed using the vertex method. The law of EV charging power decreasing with the increase in the state of charge is fully considered. To further enhance computational efficiency and model accuracy, an incremental correction method for the rolling update of the EVB feasible region is proposed, combined with the EVB event-driven incremental computing mechanism. The numerical example analysis demonstrates that the proposed method is capable of obtaining a more accurate EVB feasible region, significantly reducing the time consumption of aggregation calculation and providing practical technical support and a theoretical basis for the deep integration of EVCS into the power grid ancillary service system.