Abstract: In order to study the effects of different gases on the surface discharge characteristics of insulating materials of power electronic devices, the surface discharge current pulses of polyetheretherketone(PEEK) under positive repetitive square voltage in SF₆, N₂ and air are measured respectively, and the surface partial discharge initial voltage (PDIV), discharge current pulse parameters and average discharge time-lag of PEEK in three gases are analyzed in this paper. The results show that, under the same conditions, the PDIV of PEEK is the highest in SF₆, followed by N₂, and the lowest in air. In SF₆, the amplitude of the discharge current pulse is much smaller than that in N₂ and air, and the amplitude of the forward discharge pulse is slightly smaller than that of the backward discharge pulse. In N₂ and air, the amplitude of the forward discharge pulse is larger than that of the backward discharge pulse, and the difference is larger in N₂. The average discharge time-lag is the largest in SF₆, followed by N₂, and the smallest in air. In SF₆, the backward discharge time-lag is larger than the forward discharge time-lag, and the acceleration factor of backward discharge is larger than that of forward discharge. In N₂ and air, the time-lag of backward discharge is smaller than that of forward discharge, and the acceleration factor of backward discharge is smaller than that of forward discharge. Based on the existing research, this paper proposes a surface discharge model of PEEK in SF₆, compares the differences in the discharge characteristics under different types of gases, and explains the surface discharge mechanism of PEEK in the SF₆ gas environment.