Studying the influencing factors of insulator flashover under nanosecond pulse has important reference significance for the design of insulation structure of electromagnetic pulse simulation device. By building an experimental platform for insulator flashover, the effects of pulse voltage waveform, insulating material and surface field strength distribution on the insulator surface flashover voltage were experimentally studied in 0.5 MPa SF₆ gas. The results show that the flashover voltage of the insulator tends to increase with the decreasing of the pulse front time; Compared with the full pulse voltage wave, the flashover voltage of insulator is higher under the front waveform of pulse voltage; The insulation performance of the polyimide material is optimal; By reducing the maximum field strength along the insulator surface and improving the electric field distribution, the flashover voltage of the insulator can be effectively increased.