Abstract: Using ultrasonic testing, residual stress values can be derived from sound elastic theory, but its real feasibility is restricted because practical sonic speed is difficult to accurately measure. The comparing experimental method was adopted to analyze the relationship of sonic speed and residual stress change based on the determined relationship. The result indicated that when the inner residual stress was increasing, the sound distance was reducing in the same disposition of echo wave peak. According to the regulation, it was applicable to use ultrasonic comparing method to judge the residual stress change when only considering the stress change without considering the specific residual stress value. The proposed method showed better practicability and maneuverability.