Abstract: Lost circulation may easily occur in low pressure leaking-prone formation during cementing, so cement slurry density needs to be reduced while cementing. Using floating beads and hollow glass microbeads jointly as density lightening material and properly matching cement, stabilizer DZW and various other additives according to theory of close packing of grain composition, a low density cement slurry was designed – with a density of 1.28 g/cm3. The result of performance evaluation shows that this system can meet the requirement of settling stability, has good flowability and its filtration at 65 ℃ is less than 50 mL and its 24 h compression strength is greater than 14 MPa. Results of field application show that this composite hollow micro-bead low density cement slurry system can effectively address the problem of lost circulation in low pressure leaking-prone formation during cementing.