Abstract: Modified Phosphoaluminate Cement(MPC)is a special product which is prominently CO2-resistant,but it is unsuitable for cementing in high CO2 well because of its poor thickening performance.In the experiment,several types of conventional retarder and compounds were evaluated to determine their impact on MPC thickening;a three-component retarder based on SL,BA and CA was developed,and the x-ray diffraction was used to analyze mineral composition and retarding mechanism of MPC slurry.The results indicate that,at CA:SL:BA=1:20:20,the slurry shows higher liquidity index,smaller free fluid volume,short transit time from 30Bc to 100Bc,good right-angle effects and minimal impact on slurry strength through early to middle stages.When 0.05%CA+1%SL+1%BA was added,the thickening time of slurry was 536min,liquidity index was 0.900,and free liquid volume was 0.4% at 75℃ and normal pressure,while the thickening time became 406min at 90℃ and 15MPa,both acceptable for cementing.This composite retarder provides new technical support for researching corrosion-resistant materials and cementing in high CO2 well.