Based　on　master-oscillator　power　amplifier　structure,　an　laser　output　with　high　pulse　energy　and　high　beam　quality　is　achieved　using　a　specific　orientation　Nd:　YAG　laser　amplifier.　The　laser　amplifier　includes　three　parts,　a　seed　laser　source,　a　pre-amplifier　stage　and　a　main-amplifier　stage.　In　the　main-amplifier　stage,　a　laser　diode　side-pump　Nd:　YAG　rod　amplifiers　is　used　for　the　amplification　of　the　seed　laser.　In　order　to　obtain　a　high　beam　quality　output,　the　thermal　depolarization　losses　for　different　cut　Nd:　YAG　rods　are　simulated.　According　to　the　simulation　results,　the　[100]-cut　Nd:　YAG　rods　are　chosen　as　the　active　materials　in　the　main-amplifier　stage.　Under　the　condition　of　repetition　frequency　of　200　Hz,　pulse　width　of　25　ns,　pulse　energy　of　40　μJ　and　a　near　diffraction　limit　seed　laser　injected,　an　output　of　425　mJ　pulse　energy　is　gained　with　a　beam　quality　factor　of　1.37,　and　the　output　power　stability　of　0.81%.　©　2017,　Chinese　Lasers　Press.　All　right　reserved.