This paper proposes an optimal phase-shift trajectory control to achieve maximum efficiency for a novel input parallel output series parallel phase shift full bridge (IPOSP-PSFB) converter. Firstly, topology of the proposed converter is flexible, which can be smoothly adjusted by controlling voltage polarity of the two primary coils, so as to achieve wide voltage range. Then, a fully analytical loss model for the IPOSP-PSFB converter is established to calculate the power loss under the entire control plane. Based on the results, the optimal phase-shift trajectory is derived to achieve maximum power efficiency, where the loss of transistors and transformers are reduced obviously. Finally, a 1.2 kW/100 kHz prototype with 1700 V SiC diodes is built. The experimental result shows that the proposed converter achieves wide voltage gain range from 2 to 18.6 and improves the power efficiency by 4.4%.