Explosion accidents on oil tank take place for two times last three year in China.The simulation test on charge density and surface potential during filling gasoline into a tank has been conducted.The volume-averaged charge density was found to rise to a maximum about 20 minutes after the pump was started and then began to decrease.The experimental dada correlate well with a simple predictive model under the assumption of uniform volume charge density and ohmic conduction.The surface potential rose steadily for about 30minutes and then decreased during filling operation.The maximum of surface potential sharply increased when the filling rate rose.