Based on the diffuse wave transfer theory, a theoretical model of singly-scattered laser-induced ultrasound in time domain which contains signal source, scattering and received field is developed under the assumption of singe- scattering. Theoretical results indicate that transversal and longitudinal wave have the common scattering mechanism and the singly-scattered intensity distribution of transversal and longitudinal wave in time regime are got. Furthermore, statistical average depth and attenuation coefficient are discussed for their influence on intensity distribution. The model has given theoretical description for non-destructive evaluation and micro-structural analysis of materials.