The vibration effect induced by acoustic pressure is one of the issues for ultrasonic Doppler velocimetry measurement in small flow channels. In this paper, the vibration effect in liquid metal lead-bismuth (PbBi) is analyzed. It is found that the vibration velocity is affected by the excitation voltage, backing layer thickness, and fluid acoustic impedance. The vibration velocity increases with excitation voltage and decreases with fluid acoustic impedance. Besides, when the thickness increases from 2 to 6 mm, the vibration velocity decreases slightly, but there are no obvious changes when the thickness is more than 6 mm. Therefore, the excitation voltage should be as low as possible, and the backing layer thickness should be more than 6 mm to minimize the vibration effect. The vibration velocity presents large fluctuation in the near field, while it decreases with the transmission distance in the far field. When the excitation voltage is 36 V, the highest vibration velocity in liquid PbBi is up to 28 mm/s in the vicinity of the transducer. Thus, it may cause relatively large deviation in the transient velocity measurement and disturb the evaluation of turbulence pulsation in small flow channels.