An ultrasonic testing device and method for the connection force of interference fit. The motion control module can realize accurate positioning for the interference fit part and accurate control for motion in the circumferential direction and the axial direction; scanning increments of the circumferential direction and the axial direction are set, and the motion control module drives the interference fit part to perform circumferential and axial point scanning until the testing of the whole matching surface is completed. The ultrasonic signal measured by the point focusing water immersion probe is transmitted to a PC through a control loop in the testing process. Then the stress distribution of the matching surface is obtained through the relationship between the ultrasonic signal and contact stress Finally, the size of the connection force is calculated according to the static friction coefficient.