Abstract: In order to research the surface flashover characteristics of two typical insulating materials (nylon and synthetic glass) under hundred-nanosecond pulse in nitrogen gas, experimental device of surface flashover under hundred-nanosecond pulse was designed. The variation laws of the flashover voltage of the insulating material with air pressure and flashover distance have been researched via experimentation. The experimental results showed that the flashover voltage increased with the increasing of the air pressure. However, the flashover electric field intensity decreased with the increasing of the distance. In the same condition, the flashover voltage of PMMA is higher than that of nylon. The flashover voltage of the materials with different gas pressure and distance under hundred-nanosecond pulse were obtained via the surface flashover experiment.