The　output　average　power　of　all　-solid　-state　picosecond　amplifier　suffered　from　self-focusing　effect　existed　in　the　gain　crystals.　Through　introducing　the　compensation　element-gallium　arsenide　(GaAs)　plate,　the　damage　due　to　self-focusing　effect　has　been　avoided　and　the　suppressing　mechanism　has　been　studied　through　theoretical　analysis　and　experimental　research　for　high　peak　power　Nd:YAG　crystal　picosecond　amplifier　systems.　The　nonlinear　refractive　index　coefficient　of　GaAs　was　obtained　by　calculation,　and　the　relationship　between　the　thickness　of　GaAs　plate　and　the　length　of　Nd:YAG　rod　under　the　optimal　effect　of　suppressing　self-focusing　was　given　by　numerical　simulations.　Under　the　condition　that　the　center　wavelength　of　the　incident　picosecond　laser　beam　is　1　064　nm,　the　repetition　frequency　is　1　kHz,　and　the　peak　power　density　is　about　12　GW/cm2,　experiments　on　the　effect　of　GaAs　plates　with　different　thicknesses　(200　μm　and　550　μm)　to　reduce　the　self-focusing　damage　in　Nd:YAG　rod　have　been　completed.　With　optimization　of　thickness　of　the　GaAs　plate,　the　compensation　method　demonstrates　high　efficiency　under　high　peak　power　picosecond　pulses　condition　especially　for　Nd:YAG　amplifier.　©　2019,　Editorial　Board　of　Journal　of　Infrared　and　Laser　Engineering.　All　right　reserved.