The thermal effect of large aperture active mirror disk Nd∶LuAG ceramic laser gain medium under high power diode pump is analyzed and the wavefront distortions caused by the thermal effect is also studied. In simulation, the size of the disk Nd∶LuAG ceramic is 64 mm×6 mm, the peak pump power is 58.5 kW, the spot size of the pump is 32 mm×35 mm and the incident angle of laser beams is 15°. Simulation results show that the maximum temperature of disk Nd∶LuAG ceramic is 55.6 ℃ at pumping state, and the negative focal length is FH=-65.78 m and FV=-77.28 m in horizontal and vertical directions, respectively. The simulated wavefront distortions peak valley value is 4.33λ(the light wavelength λ is 1064 nm), which is caused by defocus mainly. On this basis, corresponding experimental facilities are set up to measure the temperature distribution of Nd∶LuAG ceramic and the wavefront distortions introduced by laser beams. Simulation results are in good agreement with the experiment. Simulative and experimental analysis results provide important references for the optimization of the pumping uniformity and the improvement of the laser beam quality of Nd∶LuAG ceramic laser amplifier system.