The accumulated surface charge of the insulators in gas insulated substation（GIS） can not only distort the electric field but also decrease the surface flashover voltage.We established a set of high-precision surface charge measurement system utilizing the static capacitive probe method and a matched three-dimensional manipulation devices based on actual 252 k V GIS basin insulator.Referring to the insulating design and flashover properties of GIS basin insulator

an effective surface flashover experimental model was set up.The experimental results indicate that no matter under AC or DC voltage

the more the accumulated surface charge is

and the more the decrease of surface flashover voltage will be.Compared to the surface flashover voltage of insulator under 50 k V AC voltage for 1 hour

the voltage under the condition of 53 k V AC voltage for 3 hours can decrease by 10.2%

while it reaches 23.0% under DC voltage

which indicates the accumulated surface charge has a significant influence on the flashover and must be considered seriously for the insulation design.The research achievement in this paper can provide meaningful reference to the insulating design of insulators in GIS and gas insulated line（GIL）.