Aiming at the defects of the narrow locked in range and the tendency to lose phase lock at the power on or a sudden change in load in the conventional ultrasonic frequency tracking system, a composed frequency tracking strategy which combines a digital fuzzy controller with direct digital synthesis (DDS) has been proposed in this paper, and the operating principle and design method have been formulated. The experimental results show that the ultrasonic system using Fuzzy DDS can realize quick and accurate frequency tracking, and it can make the system work stably and efficiently, and it improves the efficiency of the piezoelectric transducer.