To solve solid particle sedimentation of cement slurry under high temperatures, a novel low molecular weight thermal-responsive copolymer was synthesized as a suspension stabilizer by free radical polymerization. The structure and performance of the suspension stabilizer were investigated by in-situ infrared spectroscopy, ultraviolet–visible spectroscopy, etc. The results revealed that the suspension stabilizer has thermal-responsive characteristics and excellent thermal stability. After adding 0.1% suspension stabilizer, the solids suspension stability of cement slurry was improved with a density difference ≤0.02 g cm−3 under 200 °C, and cement slurry exhibited limited viscosity increasing at low and high temperatures.