Abstract: One of the key constraints for the independent development of high-voltage high-power insulated gate bipolar transistor (IGBT) devices is high-voltage IGBT device package insulation problem. The interface between the outermost polyimide (PI) of the passivation layer and the encapsulation material, silicone gel, is prone to surface discharge since the high field strength inside the device exists at the terminal passivation layer of the chip, and this location is the weak point in the insulation of the compliant press-pack IGBT device encapsulation. In this paper, an experimental platform of surface discharge characteristics of silicone gel-PI interface is established for the positive repetitive square voltage condition that IGBTs are subjected to under normal operation, and the light pulse signals and discharge pulse signals are collected simultaneously during the discharge process. It is found that the surface discharge of the silicone gel-PI interface shows several forward discharges at the rising edge of the square voltage and the high voltage plateau of the square voltage, and several back discharges at the falling edge of the square wave and the low voltage period. Based on the one-to-one correspondence between the detected optical signals in the photomultiplier and the surface discharge pulses, a method of accurate extraction of the along-plane discharge pulses is achieved, which can be adopted to extract the surface discharge pulses and to overlap the displacement current waveforms at the rising and falling edges of the square voltage. On this basis, the current waveform parameters of surface discharge pulses and the statistical characteristics of discharge instantaneous voltages are analyzed. The results show that the time parameters of surface discharge pulses in different voltage cycles are statistically independent, i.e., the surface discharge processes in each cycle are independent of each other, and the number of discharges and the pulse amplitude increase with the increase of voltage. Finally, in combination with the discharge pulse characteristics, this paper gives a qualitative explanation of the surface discharge characteristics of silicone gel and PI material under positive repetitive square voltage.