With the continuous development of aerospace technology, the demand for Hall-electric propulsion power processing units (PPUs) in spacecraft is constantly increasing, and high-gain, high-power and high-efficiency PPUs have become the mainstream direction of research. The LLC topology enables soft switching over the full load range and therefore offers broad application prospects in PPU anode power supplies. Due to its primary and secondary gain characteristics, the primary LLC brings great challenges to the resonant inductance design of the high gain converter of the anode power supply. In view of the above problems, this paper proposes an improved secondary LLC resonant topology, which retains the soft switching characteristics of the primary LLC resonant circuit while effectively solving the resonant inductor design problem, so that the PPU anode power supply has high gain performance. In this paper, the mathematical model of the secondary LLC topology is first established by using the time domain analysis method, and then the calculation method of the peak gain is given on the basis of the model, and finally the correctness of the built model is verified by a prototype and the validity of the secondary LLC circuit is verified.