Abstract: The compatibility of drilling fluid and cement slurry is poor, and pollution will occurs as long as they contact, namely liquidity deterioration of mix slurry fluid, shortage of slurry thickening time and decrease of the cement ring strength. This paper studied the impact of drilling fluid additives used in Sichuan and Chongqing on the performance of the cement slurry by single-factor. The composition of additives was characterized by infrared spectroscopy, and the structure of cement stone was analyzed by environmental scanning electron microscope. The results show that biological tackifier and polyacrylamide potassium(KPAM) can make the slurry thicken quickly; SMT, SMP-1 and JN-A will shorten the thickening time, while the effect is small within the dosage of less than 1%. The rest additives have less affect within a certain range. Then the pollution reason was analyzed. One of the important reasons is that some additives participate in cement hydration, and affect the process of slurry formation. Polymer macromolecular chains curled and adsorption bridging will make the cement slurry flocculate. The proposal of pollution mechanism provides a theoretical basis for reasonable selection of drilling fluid additives, and can reduce the pollution of drilling fluid and cement slurry.