Abstract: In the airborne 270V high-voltage power supply system, in order to prevent electromagnetic interference to other equipment, a large-capacity filter capacitor is added to the radar power input side. The moment the aircraft is powered on, a huge surge current will be generated, which will cause a surge current impact on the generator and affect flight safety. The traditional series-connected power MOSFET soft-start circuit has problems such as slow MOS turn-off and easy failure of soft-start when the input voltage is transient and the power is repeated rapidly. Based on the traditional series N-type MOSFET soft-start circuit, an improved high-voltage surge current suppression circuit is designed. This circuit is not affected by the back-end load. During input voltage transients and rapid repeated power-on, the power tube can be turned on and off in time, and the input soft-start is realized throughout the cycle, effectively suppressing the surge current. The circuit is easy to implement and has low cost. The working principle of the improved high-voltage surge current suppression circuit is introduced in detail, and a simulation model is built for simulation verification. Finally, the feasibility of the proposed surge suppression circuit is verified through experiments.