The influence due to particle contaminated on spacer surface is remarkable in the decreasing of dielectric strength in SF6 GIS. In relation with this problem, We studied, AC flash-over voltage characteristics and breakdown mechanism are investigated under metallic and insulating particle initiated condition in SF6 gas by varying the particle position, particle shape with a plane-plane electrode. The main results are as follows $circled1$ Influence of the flash-over voltage decrease for particle position is lowest in mid gap and is highest in separated small gap on electrode. $circled2$ The metallic particle shape which results in the more reduced flash-over voltage, the FOV saturation moved in to the region of low pressure. $circled3$Insulating particle less than 0.6[mm] are not almost influenced by the flash-over Voltage.oltage.