During the charging process of impulse voltage generator, the ununiformity phenomenon of charging voltage of different stage capacitors inevitably occur which can influence the accuracy of output forecast and control settings, especially for most multi-stage generators. In the paper, the mathematical analysis of the charging process is discussed using the artificial transmission line model. The simulation experiments with EMTP software and field measurement are also done. The results are compared and turned out to be quite anastomotic. Factors which can affect the ununiformity phenomenon are researched in the simulation experiment.