Diode laser arrays side-pumped Nd:YAG slab double-pass laser power amplifier is studied in the paper. Experimental results and numerical simulations of laser performance are presented. ΜΟΡΑ system has been built up using gaussian beam as source. Over 210 mJ energy per pulse green laser output at 500 Hz repetition rate is achieved Beam quality M2 is less than 6.5.The fluctuation of the laser output energy is less than 2%. The result shows that the experimental data have been consistent with the numerical calculation results.