Partial discharge is the main source generating surface charge on insulators. In order to study the dynamic process of surface charge accumulation on composite insulators

we have developed a PIC/MCC method that combines the particle-in-cell method（PIC method） and the Monte Carlo collision model（MCC model） to track the motion of electrons

in which various kinds of collisions between electrons and gas molecules

as well as the effect of special distribution of charged particles on the electric field of insulators

are fully taken into consideration. The results show that under the influence of electric field

the electrons generated from gas discharges mainly accumulate on the surfaces of insulator jacket and umbrella close to the negative electrode side. The number of electrons firstly increases and then decreases along the outward radical direction on the umbrella surface

while it decreases along the insulator jacket from the negative electrode side. The simulation results are in accordance with experimental ones

showing that the proposed PIC/MCC method is fit to simulate the dynamic process of surface charge accumulation on composite insulators.