Abstract: The measurement errors are analyzed in the measurement of bolt preload with the torque method and ultrasonic method in this paper. Based on the principles of the torque method and ultrasonic method, the measuring device is designed and the bolt preload is measured for the same type of tightening bolts with these two methods on the designed experimental device. Then bolt preload measurement error with torque method and ultrasonic method are analyzed according to the measured results. The results show that the measurement error with the ultrasonic method is lower than that with the torque method in the laboratory environment.