Abstract: Aiming at improving laser beam quality in designing high power end-pumped Nd:YAG laser, thermal lensing effect is employed to achieve high beam quality in Nd:YAG laserin this paper by placing two more Nd:YAG crystals with different doping concentrations in the resonator. Under action of pumping light, thermal lensing generated from the Nd:YAG crystal is used to shape special distribution of pump beam and fundamental mode beam. Tighter overlapping of both beams results in higher efficiency of pump power and better beam quality of laser. Experimental results show special distribution of pump beam and fundamental mode beam can be shaped by thermal lensing effectively under different pump power. Two beams are matched closely at pump power of 200 W, and M² is improved from 14.7 to 4.1.