Abstract: With the increase of the penetration rate of new energy power generation, multilevel direct current transformer(MLDT) has become the core component of realizing efficient energy conversion and interconnection due to its high efficiency, low ripple and flexible port configuration characteristics, and has been widely used in DC microgrid and flexible DC transmission system. However, the traditional control strategy is easy to cause the problem of excessive reflux power when realizing ZVS, which leads to the decrease of system efficiency and the intensification of thermal stress of power devices. To solve this problem, a full-power range ZVS optimization control strategy based on single PWM phase shift(SPWMPS) is proposed to minimize reflux power. Through dynamic adjustment of duty cycle and phase relationship, the collaborative optimization of minimum reflux power and soft switch is realized. The effectiveness of the proposed scheme is verified by theoretical analysis, simulation and experiment.