A numerical simulation study on field of temperature in crystal and melt by using FDM (Finite Differential Method) during the growth of Nd∶YAG crystal by Cz (Czochralski) method was reported. At first, the mathematical model of the growth of Nd∶YAG crystal was given, then the equations with no dimensions were given. Finally, the boundary condition was given and the equations were solved by FDM. The simulation program was given by above method, and then the change of field of temperature in crystal and melt was described by simulation program. The effect of technological conditions on field of temperature in crystal and melt was analyzed.