Frequency automatic tracking is a very important characteristic of ultrasonic power supply.Some weaknesses are found in traditional ultrasonic frequency tracking system,such as the narrow scale of frequency tracking and lose phase locked and the tendency to track frequency mistakenly,etc.This peper proposes a novel hybrid control strategy which combines fuzzy control and direct digtal frequency aynthesis(DDS).The strategy includes coarse tracking by Fuzzy controller,combined with DSP technology to realize fuzzy control and refined tracking by DDS.The results show that the ultrasonic power supply using Fuzzy DDS controller has the advantages of quick and accurate frequency tracking,and can make the vibrate system work stably and efficiently,thus it can improve power efficiency.