Abstract: To solve the cementing difficulty that the low density slurry has poor temperature stability and loss issues, and has no strength during a long period after the flowback, faced by the situation of low pressure deep well in Tazhong area cementing long vertical section with big temperature difference, it is studied that the temperature stable of low density slurry with density of 1.20~1.60 g/cm3 . The floating potential is optimized from the aspects of pressure and shearing resistance and grain morphology. Based on grain compo-sition principle, the light weight additive, filling agent, and superfine material are screened and matched, in view of improving slurry stability and pressure strength. Combining with the synergetic effect between retarder and filtrate reducer, a type of temperature stable low density slurry for long cementing sections is obtained. The results show that the slurry system has good rheology and low loss, and the density difference in the wellbore is lower than 0.02 g/cm3 . The thickening time and strength increase satisfy with operation demand, especially the cementing need of temperature difference of 70~120 ℃ and cementing length of 6 000 m with one run.