A zoom laser beam expander driven by a single hollow traveling wave rotary ultrasonic motor is proposed in this paper to meet the requirements of its dynamic continuous zoom. The moving function curves of zoom lens and compensating lens are presented based on the zoom principle. A 3D calculating model of the cam mechanism， guiding mechanism and driving mechanism of beam expander is constructed in 3D modeling software， and the theoretical analysis of force is carried out. A prototype of the beam expander is designed and manufactured， which can realize the zoom range continuously changed from 3 to 6. In order to further reduce the overall weight of the device， a type of polymer material is used as the stator of the ultrasonic motor. An experimental platform is set up to verify the performance of the prototype. The experimental results show that the presented optical beam expander has a fast transient characteristics and the positioning accuracy of the prototype is less than 0.01mm. The beam expander has realized dynamic linear zooming. With the ultrasonic motor as the driving source it can meet the requirements of rapid and high precision positioning while reducing the weight of the system.