Abstract: A nonlinear Lamb wave detection system for detecting microdefects of aluminum sheets was established. The system was used to detect the two sets of aluminum alloy test blocks after unstressed and de-stressed, and the influence of residual stress on the nonlinear effect of Lamb waves was obtained. The experimental results show that when the fatigue degree of the sample is small, the existence of residual stress will increase the ultrasonic nonlinear effect of the sample,whereas when the fatigue degree of the sample reaches 62.5% of the total life, microcracks are generated inside the sample. The nonlinear effect mainly depends on the size of the microcracks, and the residual stress has little effect on the nonlinear effect.