The sound source whichis generated by laser in liquid is studied theoretically and experimentally on the basisof the thermoelastic equition. The influence of the optical penetration depth on theultrasonical sourse is considered. In two-dimensional model, the thermal diffusion effectis neglected. From the thermal diffusion equation and wave equation, the generalexpression of displacement is given. The influence of the optical penetration depth on thesound directivity is analyzed. The theoretical curve of the sound directivity vs theoptical penetration depth is drew. In the end, the experiments testify the theoreticalresults.