The operating experience of SF6 gas insulated switchgear（GIS）shows that insulators are often the weak link and key factor of system’s insulation. Therefore it’s important to find out factors influencing flashover characteristics of insulators. Based on a steep-front impulse test device

this paper presents our study about the influence of surface conditions along insulators on their flashover characteristics. The results show that increasing the surface roughness would decrease the flashover voltage of insulators

and this phenomenon is analyzed from the perspective of surface absorption ability of insulators. Flashover voltage drops obviously when conductive particle is attached to insulator surface

and the closer the particle is to the high-voltage electrode

the lower flashover voltage becomes

which is due to the change of electric filed along insulator surface brought by the change of particle position.