Aiming at the problems of low frequency and large volume of LCC resonant topology of X-ray high voltage power supply, the main circuit design of X-ray high voltage power supply is realized by the combination of full bridge LLC resonant converter and bidirectional symmetric voltage doubling rectification. Based on the analysis of the working principle of LLC resonant converter and the output characteristics of the voltage doubling rectifying circuit, the fundamental wave equivalent model of the converter is improved. And the parameters of the main circuit are designed with the aim of improving the power supply efficiency, so as to realize the high frequency miniaturization and low ripple of the X-ray high voltage power supply. The simulation results show that the output voltage of X-ray high voltage power supply is continuously adjustable from 60 kV to 180 kV, the highest working frequency can reach 728 kHz, and the ripple rate of output voltage is less than 0.03%. The correctness and feasibility of the proposed topology are proved.