Abstract: With the increasing capacity of gas insulated switchgear (GIS) devices, it is more difficult to carry out the lightning impulse tests at the corresponding voltage level on the spot. Moreover the wave-front time of the impulse may last for ten microseconds. Therefore, in order to determine whether it is reasonable to take the long wave-front impulse voltage at the field test, we need to investigate the influence of parameters of long wave-front impulse voltage on the discharge characteristics of SF₆ gas gap and understand the discharge characteristics of insulation defects in GIS under the impact of the impulse voltage. Based on two different structures of the rod-plate electrode and the coaxial bus-pin-plate electrode, this paper mainly works on the effect of the rising rate of wave- front voltage on the discharge voltage in the SF₆ gap. The results show that the gap breakdown voltage under the two different gaps exhibits a U-shaped trend with the increase of voltage escalating rate. In addition, the research shows that the knee-point voltage of the U-shaped curve is related to the 'corona stabilization' of the space charge. Moreover, the change law of the breakdown voltage on both the left and the right half of U-shaped curve is affected by the combination of 'corona stabilization' of the space charge and the 'sweep effect' of the background electric field.