The new type of microchannel cooling laser diode arrays are used as the pump source of Nd∶YAG oscilator and Nd∶YAG slab multipass amplifier, in which the SBS phase conjugation mirror of CCl 4 is used to improve the beam quality. At the repetition frequency of 750 Hz the laser beam with the pulse width of 15 ns and average power of 180 W is obtained. The beam divergence of system is measured to be 1.5× the diffraction limit.