To make sure the half-bridge three-level dual active bridge (HBTL-DAB) circuit works correctly,the problem of capacitor voltage equalization between the upper and lower direct current (DC) buses on the three-level side must be solved. In the traditional symmetrical control mode,the capacitor voltage equalization control under load can be achieved by fine-tuning the duty cycle. However,in the case of no-load,the symmetrical control mode is difficult to realize the balance adjustment of the upper and lower DC bus capacitor voltages from the control strategy. Therefore,in view of the above problem,an asymmetric control method for the HBTL-DAB circuit is proposed. Firstly,the reason why the symmetrical mode cannot be equalized is theoretically analyzed. And then according to the asymmetric method,energy deviation on the upper and lower DC bus capacitor between positive and negative half cycles under no-load conditions is calculated. The capacitor voltage equalization control is achieved by adjusting the energy deviation,and the main factors affecting the effect of voltage balance control are also pointed out. Finally,the asymmetric control method is verified under various working conditions by simulation. The results show that no matter in condition of existing external continuous unbalance factors,or external initial unbalance factors,or internal pulse error factors,voltage balance adjustment is achieved by the asymmetric control method under no-load and loaded conditions.