According to the calculation model of the keyhole porfile, the 3D point cloud data is calculated. Then, the paper establishes a physical model of the keyhole in the laser welding by using the 3D reverse technology. The adaptive mesh generation of the model is processed by the independent development software. Finally this paper establishes a mathematical model of the temperature field in the laser welding, which considers the factor of the welding velocity. A more accurate temperature field is obtained by using the laser welding solver which is a secondary development of OpenFOAM, adding the Guass surface source and the keyhole volume source, and setting the boundary condition of convection and radiation. The result provides more accurate bases for the welding stress field.