Abstract: Earlier reports claimed that partial discharge (PD) of high frequency (HF) stress is related to the characteristic of charge transportation. However, the detailed mechanism is still not very clear. In order to understand the effect of charge transportation on PD of oil-paper, an experiment system of charge transportation for oil-paper insulation under HF stress was built based on the method of surface potential decay. The accumulation and dissipation characteristics of surface charge, as well as the characteristics of trap distribution were studied. The trap density of oil-paper was quantitatively calculated. Then, the influence mechanism of charge transportation on PD of oil-paper insulation under HF stress was analyzed. The results show that the initial surface charge decreases from 1856.6 V to 1017.8 V with the increase of frequency. The decay rate of surface charge firstly increases from 68.5 % to 80 % then decreases to 65.9%. The total trap density shows a downward trend from 1.82×10³⁸m^-3 to 9.99 ×10³⁷m^-3. The trap depth decreases at first and then increases. In addition, the mechanism of charge transportation is an important reason for the change in the discharge characteristics of HF oil-paper insulation.