LC series resonant high voltage constant current charging power supply can realize high efficiency and fast charging of the capacitor and has an excellent capacity of anti-load short-circuit, hence it has extensive application prospects in high repetition frequency pulsed power systems. The efficiency of the charging power supply is a crucial factor to determine the ability of the system to operate at repetition rate. Improving efficiency is the primary goal of designing high-voltage capacitor charging power supply. According to the working principle of LC series resonant circuit, it is analyzed that the operating mode of power supply, the switching frequency of the inverter bridge and the distribution parameters of the high-frequency transformer are the main ingredients affecting the efficiency. For a DC power supply with a power of 10 kW and an output voltage of 40 kV, the main circuit parameters were calculated and the circuit model was established using Pspice to verify its accuracy. The soft switching technology was used to reduce the switching loss, and the high frequency transformer with smaller distribution parameters was designed to further improve the efficiency. On this basis, the overall structure design of the power supply was completed. Finally, the charging characteristics of the power supply were tested. Experimental tests indicate that the power supply can charge a 0.1 µF capacitor to 39.5 kV within 37 ms, and the charging efficiency of the power supply is 87.1%.