Electric vehicle （EV） charging stations utilize their remaining reactive power capacity to provide auxiliary services to the power grid, assisting in achieving automatic voltage control （AVC） and generating additional revenue for the charging stations. In this paper a market mechanism for the voltage regulation auxiliary services of EV charging stations is proposed, the circuit topology of charging piles within the charging station is established, and the basic principles of reactive power support by charging piles are analyzed. Based on this, using probability statistics and the Monte Carlo method, considering the charging demands of electric private cars and electric taxis, the charging behaviors of each are simulated. Combined with power constraints of the charging piles and transformer capacity constraints, the daily load distribution curve of the charging station is predicted. Furthermore, the reactive power support capability of the charging station within a day is evaluated and the revenue obtained from the participation of the charging station in voltage regulation auxiliary services within a day is calculated. Sensitivity analysis of relevant parameters of fast-charging piles within the charging station is conducted, highlighting the differences in reactive power support capabilities corresponding to different parameters of EV charging stations. This provides technical analysis tools for charging stations to declare their participation capacities in voltage regulation services and obtain relevant compensation benefits.