Abstract: The nonlinearity in ultrasonic guided waves was treated as a second-order perturbation of the linear wave motion response.Based on the approaches of second-order perturbation approximation and modal expansion analysis for waveguide excitation,the effect of second-harmonic generation of primary (fundamental) ultrasonic guided wave propagation in an anisotropic solid plate has been studied theoretically.The general formal solution to second-harmonic displacement field of primary ultrasonic guided waves has also been presented.It was found that the elastic anisotropy of the plate material might,in several aspects,influence the effect of second-harmonic generation of guided wave modes. Especially,the changes in the phase velocities of guided waves,caused by the elastic anisotropy of the plate material, might clearly influence the degree of accumulative growth of double frequency guided wave modes,constituting the field of second harmonic of primary guided waves,with propagation distance.In terms of the results of theoretical analyses and numerical calculations,it was known that there was obvious difference in the nonlinear effect of ultrasonic guided waves in different directions of propagation,and that the second harmonic of primary guided wave propagation was highly sensitive to the elastic anisotropy of the plate material.The results obtained might provide a theoretical basis for accurate characterization of the elastic anisotropy of the plate material by using the nonlinear effect of ultrasonic guided wave propagation.