Abstract: The cement fluid loss reduction additives used in China generally have the deficiency of weak salinity tolerance and poor thermal stability. To solve this problem, considering molecular structure, excellent performance monomers were selected, and then the salt tolerant and thermostable fluid loss reduction additive DRF-120L was prepared according to free radical polymerization in aqueous solution. DRF-120L is a type of copolymer and its main chain contains sulfonic group and dicarboxyl groups, which improves the adsorption capacity to cement particle, so the capacity of controlling fluid loss was improved. The initiator amount, reaction temperature, monomer mass fraction were investigate, and the optimum polymerization conditions was determined. Finally DRF-120L was synthesized with temperature resistance of up to 200 ℃.API fluid loss both in fresh water cement slurry and saline water cement slurry can be controlled under 100 ml under high temperature. DRF-120L has little effect on development ofcement strength under high temperature. Both conventional density cement slurry and high density cement slurry mixed mainly with DRF-120L have good comprehensive properties. Therefore, DRF-120L can satisfy the requirement of high temperature and deep well cementing.