In order to acquire the high beam quality output laser, the high beam quality laser seeder is obtained by the method of twist mode. At the same time, compensation of birefringence, uniform pump cavity and phase conjugation mirror （PCM） were used to improve the beam quality of MOPA laser system. More than 4（10 mJ, 40 Hz output laser with near diffraction limited beam quality was obtained. And it is very useful to design the high power laser.