Aiming at the difficult problem that the surface defects is quantitatively detected by the non-contact NDT methods,the interaction between laser-induced Rayleigh wave and surface defects has been simulated by the finite-element method. The time-dependence relationship between Rayleigh reflected wave and surface defect depth was studied. The time domain feature quantities that can quantitatively character the defect depth were extracted through analyzing formation mechanism of time-dependence relationship,and the mathematical relationship of time domain feature quantities and surface defect depth was deduced. The depth of surface defect was calculated by using the mathematical relationship in surface defect detection of laser ultrasonics. The results show that the experimental results match well with the numerical simulation results,and it is a linear relationship between the time-domain feature quantities and surface defect depth. The time-domain feature quantities of reflected Rayleigh wave can achieve the quantitative detection of surface defect depths with the range of 0.1~0.5 mm,and the maximum error is less than 0.06 mm.