Abstract: The preparation of uranous ion from uranyl nitrate at different current densities (40-160 mA/cm²) was investigated in this paper. The results show that membrane electrolysis can ensure high uranyl conversion ratio and maintain high current efficiency during most time of the electrolysis process. However, in the latter part of the process (most of the uranyl ions are converted to uranous ion), when current density is high, current efficiency declines rapidly; low current density is beneficial to maintain high current efficiency. Therefore, a preprogrammed automatic control for a step decreasing current density was studied to improve the current efficiency further. Compared with the constant current density, the step decreasing current density can effectively improve the current efficiency of the electrolysis process and reduce side reactions.