The temperature thermal model of crystal was built under the condition of thermal isolation of the end face and constant peripheral temperature, so as to calculate temperature field of pulse LD end-pumped Nd:YAG crystal. Based on the function of temperature of the laser crystal depending on the thermal conductivity, the thermal model of heat conduction equations were solved by methods of the secant method. The numerical values of the temperature field of the pulse LD end-pumped square cross section Nd:YAG crystal with variable thermal conductivity was obtained. Then the internal temperature field distribution was calculated under different of super-Gaussian beam with different orders and pump spot sizes. The results show that when the average output power of diode laser is 60 W, and the neodimium doped yttrium aluminum garnet with 1.0% neodymium-ion doped mass fraction, the third order super-Gaussian radius of incident light is 400 μm. When the transient temperature field of Nd:YAG crystal, which size in 4 mm×4 mm×8 mm, reaches thermal dynamic equilibrium state, the maximum and minimum temperatures are 364 K and 337 K respectively. The research methods and results can also be used to analyze other time-varying thermal problems in laser systems, and will play theoretically a directional role in solving thermal problems in laser systems.