The necessity of the noise reduction on longitudinal critical refraction（LCR）wave for measuring the residual stress of A7 N01 aluminum alloy and S355 J low alloy steel are analyzed. And the calibration processes of A7 N01 and S355 J are respectively realized by the method of stretching, and the local details of noise reduction signal and noise signal are compared,and the calibration result of noise reduction signal and noise signal is finally proposed. Above experimental analysis shows that the influence of stress on the characteristics of ultrasonic transmission in aluminum alloy is more obvious. Noise reduction is very necessary for the stress in S355 J measured by LCR method,while the noise reduction can be ignored for the stress test of A7 N01.