Based on typical structure of voltage source converter based HVDC (VSC-HVDC) station and its parameters, the impact of startup process of VSC-HVDC station on AC grid is analyzed in this paper. According to the characteristic of voltage and current during station startup, it is concluded that AC grid voltage might drop abruptly because of transformer excitation inrush current or incomplete charge of DC capacitors at the time of closing AC circuit breaker or bypassing charging resistor. A control method to avoid the voltage drop of AC grid is proposed which decreases over current through phase selection switchs and delayed charging resistor bypassing. The method is verified through simulations based on real VSC-HVDC station.