A diode pump high power and high efficiency Nd∶YAG planar waveguide oscillator at quasi-continuous mode is reported. The 1 mm×10 mm×60 mm planer waveguide is selected as gain medium. The plane-plane cavity is built, and the output properties of the planar waveguide laser under different output mirror transmissions and different pulse repetition rates are studied. Experimental results show that when the output coupler transmission is 79%, an average output power of 441 W for the 1064 nm laser is achieved under the pulse repetition rate of 500 Hz and the drive current of 200 A. Under five different repetition rates, the maximum single pulse energy is 928 mJ, and the effective optical to optical efficiency is 53.2%. The pulse waveform of output laser is consistent with that of the pump laser, and both have a pulse width of 240 μs. The output power of the oscillator can be increased after the system optimization.