A rotary varifocal mechanism driven by ultrasonic motor was designed to remedy the shortcomings of a traditional varifocal mechanism in moving along the axial or radial directions,such as large occupation space, complicated configuration, long time consumption, low control precision, and the lack of self-locking function.This new varifocal mechanism has the advantages of the small space, simple configuration, short time for zoom completed, high control precision of rotating angle, strong repeatability, and self-locking function. The results of 100 shutoff characteristics of repeatability experiments show that the longest and the shortest shutoffs are 0.756 ms and 0.748 ms,respectively, when the average rotation speed is 150 r/min. Therefore, the maximum error of the shutoff time is 0.008 ms, the largest rotating angle error of the rotary varifocal mechanism is 0.432′,and the largest angle error displacement in the imager is less than 0.015 mm.These data can meet the system requirement.