Based on the basic performance requirements of cement slurry in deep and ultra-deep wells in Tahe peripheral blocks and considering the effect of high temperature and high pressure on the cement slurry performance, by analyzing the mechanism of thermostable materials, the additives suitable for thermostable cement slurry are selected. The retarder, fluid loss additive, nano liquid silica and some other thermostable materials are mixed according to the requirements to carry out the research on thermostable（≥120℃）cement slurry system with different density and measure the regular properties. This series of cement slurry, with the characteristics of good fluidity, API filter loss less than 50mL, anti-gas-migration coefficient SPN less than 1, high temperature stability and high compressive strength of the set cement, can meet the technical requirements for high temperature and high pressure underground construction. This series of thermostable cement slurry have been used in the cementing of the well-SHBP1H， well-SHB7 and well-Zhongtan1 with high excellent rate.