Abstract: In this paper, a copolymer cement suspension agent was developed in order to solve problems found in deep wells, such as high temperature and settlement stability of cementing slurry. The terpolymer (AMPS/AM/NVP) cement suspension agent was synthesized with 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylamide (AM) and N-vinyl-2-pyrrolidone (NVP) as comonomers by means of free-radical aqueous solution polymerization. And its optimum synthesis conditions were confirmed on the basis of orthogonal test results. Its structure was analyzed by means of infrared spectrum analysis and nuclear magnetic resonance spectroscopy. Based on thermal analysis, it was thermally stable. Further, it was demonstrated by performance test results that based on this copolymer suspension agent, that the settlement stability of cement slurry at 200℃ could be kept below 0.01 g/cm3, with free fluid 0. Further, there was enhanced saturated brine tolerance. The new copolymer suspension agent could meet field requirements comprehensively in terms of thickening, filtration, rheological behavior and strength. It was demonstrated by field tests of three wells that this kind of new high-temperature cement suspension agent played an effective role in improving the safety and quality of cementing operations in deep wells.