Abstract: Towards the safety operation of metal plate structure,a nonlinear Lamb wave mixing method was develop for fatigue detection in metal plates.The numerical simulations were conducted to investigate the nonlinear interaction between the two A₀ Lamb waves and the material nonlinearity.The results show that two collinear A₀ Lamb waves produce a sum frequency S₀ wave which propagates in one direction at the damaged structural material,and the amplitude of the sum frequency wave exhibit a cumulative growth effect with the propagation distance.Co-linear Lamb wave mixing experiments were conducted on metal plate specimens with different fatigue levels.The results showed that the amplitude of sum frequency wave showed a monotonic increasing trend with the increase of fatigue cycles of the specimen,and the proposed Lamb wave mixing technique can be used to characterize the fatigue degree of metal plates.The research provides a feasible solution for fatigue evaluation in metal plates.