The shunt active power filter(APF) with diode?clamped three-level?topology is chosen as research object in this paper. Aiming at problem of the midpoint voltage imbalance on the DC side, the traditional balancing methods are analyzed deeply and then a novel hardware midpoint-voltage control method is put forward. Simultaneously three kinds of midpoint-voltage control methods are applied in three-level APF, and simulation platform is built. Simulation results verify the feasibility of above control method based on the hardware midpoint-voltage balance.