Abstract: Aiming at quantitative identification of defects in structures,the scattering characteristics of defects in structures are studied.The scattering simulation model of elliptic defect is established and the effect of defect deflection angle and size on the de-correlation of scattering signal is studied.The results show that the de-correlation coefficient matrix of ultrasonic signal has a great correlation with the defect geometry state(such as size and angle),but it is not a simple linear correlation.On this basis,combining the parametric finite element analysis and Bayesian theory,a defect inversion method based on ultrasonic scattering signal de-correlation analysis is developed,and the numerical simulation and detection experiments of defect inversion are carried out.The results show that the developed defect inversion method can well realize the inversion of the position and size of defect in aluminum block and plate.The inversion error of the open defect size(depth) of the aluminum block is about 0.2 times of the excitation wavelength,and the position error is about 0.6 times of the excitation wavelength.The inversion error of the circular defect size of aluminum plate is about 0.04 times of the excitation wavelength,and the position error is about 0.4 times of the excitation wavelength.The research work has made a beneficial exploration for the quantitative identification and evaluation of defects in structures.