Abstract: The dispersion,the mode shape and the power flow density of guided waves in a orthotropic viscoelastic composite plates is studied.Based on two-dimensional eqquations of motion,the dispersion equation is obtained using spectral finite element method.The effect of anisotropy and viscosity to the energy velocity and the mode shape of guided waves have been studied in the orthotropic viscoelastic plate,as well as the effect of substrate to the power flow density of the guided waves has been analyzed.The results showed that the maximum energy velocity is obtained when the guided waves propagate along the fiber orientation;the viscosity of material has little effect on the velocity but decreases the amplitude of mode shape;due to the presence of substrate,the power flow density of two fundamental mode concentrates to the upper and lower surfaces of the waveguided in the high-frequency range,which form a weak dispersion,high attenuation and a non-dispersion,non-attenuation surface waves,respectively.The numerical result provides a theoretical basis of guided waves for quantitatively non-destructive testing and performance evaluation of composite materials.