We　report　an　effective　method　to　reduce　the　impact　of　polarization　state　changes　caused　by　thermal　birefringence　in　intra-cavity　frequency-doubled　laser.　The　laser　consists　of　a　diode　side　pumped　Nd:YAG　module,　an　acousto-optic　modulator　Q-switch,　and　an　LBO　crystal　used　for　SHG　generation　in　532　nm　laser.　The　effect　of　thermal　birefringence　originated　by　the　Nd:YAG　rod　with　concave-shape　end　surfaces　on　SHG　efficiency　is　compensated　by　the　insertion　of　a　lambda/8　plate　into　the　cavity.　At　the　repetition　frequency　of　9　kHz,　the　532　nm　laser　achieves　a　maximum　output　power　of　23.8　W,　a　pulse　duration　of　60　ns　(FWHM),　and　a　beam　quality　factor　of　Mx　2　x　My　2　=　1.52　x　1.43.　Compared　with　the　lambda/4　plate　and　without　plate,　the　maximum　average　power　of　the　laser　with　the　lambda/8　plate　has　increased　by　22.7%　and　66.4%,　respectively,　the　beam　quality　factor　has　also　been　greatly　improved　correspondingly.　This　method　provides　a　new　solution　for　lasers　to　compensate　thermally　induced　birefringence.