This thesis presents results of study and implementation of half bridge resonant power supply with active power factor correction. First, active power factor correction approach was discussed to rectify the wave form distortion of bridge current and realize high power factor, high efficiency and low current harmonics. Afterward, it gave a stable high quality dc power input for half bridge resonant power supply. Second, half bridge resonant power supply could achieve Zero Voltage Switching (ZVS) in the switching process to reduce power losses. When the variable frequency control was used for tracking the resonant frequency, this process also helped keep the system operated at the optimal condition. Finally, the realizations of power supply system was implemented, measured and analyzed under load variations. The power supply was operated under 90Vac~264Vac input voltage range and 24Vdc / 10A was measured as an output. The experimental results showed that an optimum efficiency of proposed system can reach up to 92.96% at the input voltage of 264Vac.