Electric vehicle charging stations, as typical nonlinear loads connected to the distribution network, are prone to cause power quality problems such as harmonic pollution and voltage fluctuations. This article constructs a three-phase six-pulse rectifier circuit model, analyzes the load characteristics and harmonic generation mechanism of the charging station, proposes the concept of "harmonic phase Angle distribution entropy", and develops an improved particle swarm optimization algorithm to optimize the access strategy. The simulation results show that the ordered access strategy can reduce the total harmonic distortion rate from 3.67% to 2.30%, which can effectively improve the power quality.