Abstract: The high voltage DC power supply is the key component of the nuclear radiation detector, such as the ionization chamber. For the ionization chamber that needs about 3 kV high voltage, a miniature high voltage DC power supply with low noise, high efficiency and high stability was designed in this paper, which can adjust from 0 V to 3 kV. The high voltage DC power supply system was designed by using hybrid mode with linearity and switch, and it is a compromise between the conversion efficiency and low noise. The core boost conversion circuit adopted linear resonant Royer circuit and high-frequency transformer to ensure sufficiently low output ripple. The power of resonant Royer circuit was provided by ultra low noise switching regulator LT1534, which can control transition time while achieving the design of hybrid mode high voltage DC power supply. The ripple of output voltage is further reduced by using the two-step RC filter circuit. The measured output voltage range is from 0 V to 3 kV, the static power is 0.4 W, and the ripple of 3 kV output voltage is 16.55 mV. It shows that the power supply can be used for the nuclear radiation detector of low noise.