Pumped with Xe-flashlamp will induce non-uniformity rising of temperature in the Nd:glass and brought wave-front distortion with low space frequency,which is the main aberration source of the amplifier. So the wave-front distortion of the assembled slab amplifier with 400 mm aperture is studied in this text. The calculating results indicate that,with presently pumping configuration,the temperature rise of the Nd:glass is about 0.85 ℃,the non-uniformity temperature distributing induced “S” shape distortion is about 1.7×10-6 m,and the thermal-stress is about 65 kPa,the total wave-front distortion is about 0.3λ,which matched the experiment value of the Lawrence Livermore National Laboratory (LLNL). With presently pumping configuration,pump-induced wave-front distortion is acceptable.