The DC power distribution system usually adopts bipolar power supply mode,which is suitable for occasions with independent positive and negative load and high reliability requirements. In order to realize the application of power electronic transformer in real bipolar low voltage DC system, a power electronic transformer topology based on switching multiplexing sub-module is proposed,and its working principle and control strategy are analyzed. The proposed power electronic transformer control includes low-voltage port voltage control and voltage equalization control. The voltage equalization controller and the low-voltage port voltage controller are mutually decoupled to facilitate independent design. Compared with the traditional true bipolar wiring form,the effective multiplexing of power switches between double active bridges and voltage equalization circuits in the proposed sub-module effectively reduces system cost and improve power density. The simulation results verify the correctness and effectiveness of the proposed control strategy.