A novel constant power control strategy of electronic ballast for electrodeless fluorescent lamps is proposed in this paper. The micro-controller samples the lamp voltage and current, and calculates an appropriate value of lamp power. The digital controller controls PWM dimming level corresponding to the power requirements. Thus, the constant power can be approached. The digital-analog mixed control circuit is low-cost and reliable. A novel algorithm is proposed which can make a power regulation more accurately and ensure a high precision of the lamp power.