Abstract: The domestic X-ray high voltage power supply is generally larger, and it isn’t suitable for the requirement of micro X-ray tube. For the characteristics of micro X-ray tube, a miniature high voltage power supply of low ripple was designed in this paper, and its output voltage is adjustable from 0 to -40 kV. The inverter circuit adopted resonant Royer circuit. In order to improve circuit efficiency, UCC2973 was introduced. A high frequency transformer and bidirectional voltage doubling rectifying circuit were designed in boost circuit in order to do the two-stage booster. The way of voltage regulation was voltage feedback after resistive subdivision. With working on the linear condition, it had no switching noise. The testing results show that the output voltage ripple is less than 0.3% and stability is better than 0.12%/10 h, and the high voltage power supply meets the requirements of micro X-ray tube.