In recent years, China’s high-speed railway has pursued higher speed and greater capacity. Trains automatically disconnect the vacuum circuit breaker (VCB) when approaching the neutral section (phase-split zone), and re-close the breaker to restore power supply after driving away. When switching on and off the VCB, it generates high-frequency and high-amplitude overvoltage, which threatens the safety of vehicle-mounted equipment. To improve transportation efficiency, multi-train reconnection often involves multiple VCB operations, exacerbating the impact of overvoltage. In this paper, the overvoltage mechanism under switching on and off operations is analyzed, establish a single-train/multi-train traction power supply system model, and verify the model's accuracy. The effects of distributed capacitance and protective grounding impedance on overvoltage are analyzed, as well as the effects of the time interval and phase on overvoltage during multi-train reconnection. The results show that the overvoltage amplitude of the rear car is exacerbated by the short switching interval between the front and rear cars. Based on the above analysis, suppression schemes such as adjusting train equipment parameters, shunt capacitors, and switching time intervals are proposed. It provides a reference for the overvoltage suppression of trains under multi-train reconnection in engineering practice.