In　this　paper,　on　the　basis　of　the　theory　of　quasi　phase　matched,　CO2　laser　spectrum　corresponding　to　GaAs　chip　within　the　scope　of　the　matching　length　was　calculated.　Through　the　numerical　solution　of　the　wave　equation,　the　relationship　between　power　density　of　pump　laser　and　frequency　doubling　conversion　efficiency　was　given　under　the　different　crystal　length　conditions.　By　adjusting　the　CO2　laser　gas　mixture　components,　we　optimized　the　pump　laser　pulse　wave　to　meet　the　requirements　in　the　temporal　distribution　of　the　pump　light.　On　the　other　hand,　we　optimize　the　output　beam　mode　to　meet　the　pump　light　distribution　in　space　requirements.　We　use　the　tunable　TEA　CO2　laser　as　the　light　source　to　pump　quasi　phase　matching　GaAs　crystal,　When　the　pump　wavelength　is　changed　from　9.23　mu　m　to　10.75　mu　m　range,　the　conversion　efficiency　of　frequency　doubling　output　is　greater　than　4%,　when　the　pump　wavelength　is　10.68um,　the　frequency　doubling　efficiency　reached　6.58%.