In order to quantitatively detect the physical properties and structural parameters of subsurface defects in materials by photothermal radiation technology, the finite element analysis method is used to simulate the steady state fluctuation temperature field of the material containing defects. An empirical formula for determining the depth and boundary of blind holes is proposed by analyzing the photothermal radiation signals. The relationship between photothermal radiation signals and defect shapes and thermal properties is revealed. The diameter and depth of the flat bottom blind holes with diameters of 1.5 mm, 2.0 mm, 2.5 mm, and depths of 0.2 mm and 0.4 mm, respectively, are measured by photothermal radiation techniques. The experimental results show that the diameter detection error is less than 15%, and the depth detection error is less than 10%. The effectiveness of the method for quantitative detection of defects by means of finite element analysis is verified by photothermal radiation detection experiment.