Total Focusing Method (TFM), as a kind of post-processing imaging method, has attracted researchers’ attention due to its better resolution and high signal-to-noise ratio (SNR) in comparison to traditional imaging techniques. However, without analyzing the properties of damage scattering, the TFM algorithm fails to realize the quantitative evaluation of the damage. On the purpose of improving imaging sensitivity and SNR, an ultrasonic scattering model is developed which takes into account the interaction between the incident ultrasonic fields and the damage, then the reflectivity of the damage surface can be obtained. Finally, the imaging of the reflectivity of the damage is formed by using this inverse scattering model in frequency domain. Because of the advantages of non-contact, non-destructive and couplant free, laser-generated ultrasound is used as an excitation method in the model. In this paper, the finite element models of ultrasonic propagation in damaged structures are carried out. The damage types are circular holes and cracks of different sizes. The simulation results show that the TFM algorithm combined with the inverse scattering model can locate the damages accurately, and the size as well as the orientation of the cracks can also be identified quantitatively. The proposed model obviously enhances the image sensitivity and SNR, which proves its ability of small damage location and characterization.