During the process of well cementing in deepwater, the cement slurry experiences a wide range of temperature variation from low temperature at seabed to high temperature in downhole. The elevated temperature affects the rheology of cement slurry. The change of rheology of cement slurry could influence the safety of cementing operation. The aim of this paper is to develop a new kind of hydrophobically associating water-soluble polymer (KWHL-1) as an additive to prepare a constant rheology oil well cement slurry, which can be used at temperature range from 4℃ to 90℃. The acrylamide, 2-acrylamide-2-methylpropionic acid and stearyl methylacrylate were applied to synthesize the KWHL-1 by the inverse microemulsion polymerization. Test results indicate that the critical association temperature of KWHL-1 is 45℃. The critical association temperature is independent with KWHL-1 concentration, salt concentration and alkalinity of solution. When the temperature is below 45℃, KWHL-1 shows little influence on the viscosity of solution. When the temperature is above 45℃, the KWHL-1 forms spatial network structure by intermolecular hydrophobic association, and thus increases the viscosity of solution significantly. The KWHL-1 also displays good thermal stability and excellent salt and alkali resistance properties. In addition, the KWHL-1 shows nearly no negative influence on the basic properties of cement slurry, which indicates that the KWHL-1 can be used as a constant rheology agent to prepare a cement slurry with constant rheology in the temperature range of 4 to 90℃.