In this paper, an atmospheric pressure plasma power supply with constant power control is analyzed and implemented. A series resonant network with step up transformer is designed to provide 3kW and 5 kVrms∼7.5 kV rms for atmospheric pressure plasma power supply. The equivalent circuit model of the plasma reactor is derived and the operating principle of the series resonant inverter is discussed. Also, a digital signal processor is used to control the phase shift angle of the series resonant inverter and achieving constant power control with very simple algorithm. The operating frequency of the full bridge series resonant inverter is higher than the resonant frequency so that the zero voltage switching (ZVS) can be achieved and the efficiency can be increased. Finally, a power supply with 3 kW and 5 kV rms∼7.5 kVrms is implemented in the laboratory. In addition, an auxiliary winding of step-up transformer is added so that the maximum voltage is limited and the under voltage condition operating can be avoided. The experimental results reveal that the plasma reactor can be controlled at the designated value and the maximum efficiency is 91.34% at 1.8 kW/6.34 kVrms.