The temperature field distributions of three Nd∶YAG crystal structures were calculated by using the Comsol multiphysical field simulation software,and the output power and conversion efficiency of the composite crystal and the uniform doped Nd∶ YAG crystal were compared through the experiments.The simulation results show that the maximum temperatures of three crystals whose size are 3 mm×3 mm×10 mm、3 mm×3 mm×16 mm and 3 mm×3 mm×20 mm are 97.12 ℃,89.08 ℃ and 88.01 ℃ respectively when pumping power is 18 W.The composite crystal has an obvious advantage in reducing the temperature of the crystal and reducing the thermal effect.When pumping power is 18 W,the maximum output power of uniform doped Nd∶YAG crystals is 6 W,while the output power at 1064 nm with the 16 mm composite crystal is 9.3 W.Meanwhile,there is no saturation phenomenon for the composite crystal,and the beam quality is better than that of the uniform doped crystal.The theoretical and experimental results show that the composite crystal has a higher practicability in reducing the thermal effect.