Abstract: In order to describe the relationship between the depth and the density of foamed cement slurry,the behavior of foamed cement slurry density at different temperature and pressure was investigated.Based on the equation of state of real gas,considering the effect of temperature and pressure on foamed cement slurry density,a mathematical model of foamed cement slurry density at different temperature and pressure was set up.By laboratory the mathematical model was verified and corrected,and a mathematical model which could quantitatively calculate the foamed cement slurry density at any depth was worked out.By the implicit function integral on the revised model,foam cement slurry density at any depth of the well and hydrostatic pressure could be calculated.The revised model,considering the effects of temperature and pressure as well as the bubble volume in cement slurry on density,lays solid foundation for cementing design with balanced pressure.