Abstract: Aim at the deficiency of plate structure online stress monitoring,a new method of online stress monitoring based on the theory of acoustoelasticity for guided wave was proposed.The disperse curves and mode shapes were calculated for 4 mm Q235 steel plate based on equations of acoustoelastic motion and Rayleigh-Lamb frequency,and relative variable ratios of group velocity were calculated in theoretical equations and finite element simulation for different frequencies.Resultsshow that S0 mode is more sensitive than A0 mode and SH0 mode for acoustoelastic effect,and the optimal excitation frequency range for acoustoelastic effect is 90-150 kHz that is weak dispersion;acoustoelastic effect is related with mode shapes of excitation mode,and the larger the in-plane displacement,the more significant is the acoustoelastic effect.