We　studied　the　surface　roughness　of　chamber　sidewall　in　the　PMMA-base　microfluidic　chip　which　was　cut　with　CW　CO2　laser　at　different　laser　parameters　and　ambient　temperature.　Our　observations　show　that　the　surface　roughness　is　mostly　resulted　from　the　residues　near　the　laser　cutting　edge,　which　are　produced　from　bubble　bursting.　In　order　to　improve　the　quality　of　the　cut　surface,　we　proposed　to　preheat　PMMA　plate　to　a　suitable　temperature　before　laser　processing,　and　found　that　would　obtain　better　surface　roughness　at　70°C-190°　C.　The　best　result　in　our　experiment　was　Ra　=　100.86　nm　when　preheat　PMMA　plate　to　85　°C　in　the　water.