In DC/DC converter applications, the conflict between efficiency and wide voltage range has been a key problem to solve. In this paper, a cascaded DC/DC converter topology based on a three-level boost converter (TLB) and Serial-Half-Bridge LLC resonant converter (SHB-LLC) is proposed and an appropriate control strategy is developed. Firstly, the operating principles of TLB and SHB-LLC are analyzed separately. Secondly, the control strategy of the cascade converter is proposed. TLB adopts a dual-loop control strategy of voltage loop and voltage equalization loop to achieve wide-range voltage regulation. SHB-LLC adopts a fixed frequency and directly controls the duty cycle to achieve the soft-switching characteristics and improve the converter efficiency. Finally, a simulation model is built using Simulink. The simulation results show that the control strategy proposed in this paper can extend the input voltage range of the DC/DC converter and achieve the soft switching characteristics over a wide load range, which verifies the effectiveness and feasibility of the strategy.