Quantitative nondestructive testing (QNDT) is required for the in-service inspection of high-cost structures whose failure could lead tragic consequences. The optical methods are widely used for NDT and NDE. However, most of them base on the qualitative detection of the partial fringes induced by the defects. The defect characteristic parameters (DCPs), such as coordinates and types, are easily obtained, but it is difficult to obtain other parameters, e.g. the defect size and embedded depth due to the non-unique relation between the DCPs and the deformation of detected defects. In this paper, the optical method, design optimization and FEM are combined to accomplish QNDT. Three types of defects are inspected and their DCPs values are obtained quantitatively. Moreover, factors that influence detection accuracy of the DCPs are also discussed.