In order to realize the quantitative detection of subsurface defect width by laser ultrasound technology at different temperatures,the finite element method is employed to simulate the interaction of subsurface defect with laser-generated surface waves in the paper,and then a method to calculate the width of the subsurface defect using surface waves is presented. First,surface waves are first generated on one side of the subsurface defect and then on the other side. Finally,incident and reflected surface waves from subsurface defect are detected on both sides of the defect in the two detections,respectively. When the subsurface defect is within a wavelength range of the surface wave,the subsurface defect width can be calculated based on the arrival time of incident and reflected surface waves. The numerical results are in good agreement with the theoretical results,which provides a very effective numerical method for quantitatively calculating the subsurface defect width using laser ultrasound technology at high temperature.