Ti45nb is a commonly used titanium alloy with high strength for aviation. However, it is mainly cold formed under conventional conditions and cracks often occur when deformation is large. Ultrasonic vibration-assisted compression test of Ti45Nb titanium alloy was carried out on a universal testing machine equipped with an ultrasonic vibration system. The influence of ultrasonic vibration on the deformation behavior of Ti45Nb was investigated. The results showed that ultrasonic vibration can significantly reduce the flow stress in the deformation process, and the reduction amplitude increases with the continuation of the compression process. The decrease in flow stress is caused by the stress superposition and acoustic softening effect. Compared to the conventional compression test, the grain in the center of the ultrasonic vibration-assisted compressed sample is finer, and the thickness of the lamellar substructure in the shear band is thinner. Therefore, ultrasonic vibration has a promoting effect on the deformation of Ti45Nb alloy.