The formulas for the length and angle of surface crack are obtained based on the difference of propagation time of Rayleigh wave and the diffracted Longitudinal wave. Propagation rule of Rayleigh wave is analyzed in accordance with different depths and angels of surface cracks using the finite element method. The simulation results were validated calculations and the simulation accuracy is proved. Results indicatevia:1) During propagation of Rayleigh wave, a proportion propagates along the medium surface (including the crack surface); The remaining is subjected to mode conversion phenomenon, and becomes the diffracted transverse and longitudinal wave. All of the elastic waves are absorbed by the viscoelastic artificial boundary when they come to the border of the medium, which eliminates the influence of the reflected wave. 2) Calculation errors of the length and angle of surface crack are substantially below 5%. Within certain ranges, the calculation accuracy is higher as the values of lengths and the angles of the surface crack increase.