To analyze the performance of inverse inchworm motor under different preloads, experiments are carried out based on an inverse piezoelectric inchworm motor researched and manufactured before. In the experiments, the clamping force is used to describe the preload indirectly. The clamping forces, no-load characteristics and load characteristics of the inverse piezoelectric inchworm motor are tested under four different preloads. The results show that the driving force increases first and then decreases with the increasing of preload. When the preload is low, the high velocity of motor is 1.43 mm/s, but the driving force is low. When the preload is high, the performance of inchworm motor becomes worse. The best performance can be reached under proper preload and the maximum driving force is 2.1 N. The amplitudes of vibration of driving part have been tested with different driving frequency. When the frequency is high, the amplitude of vibration decreases, and the velocity of motor first increases and then decreases with the increasing of frequency.