The low-density cement slurry often had the problems of poor compression resistance，bad stability and low compressive strength. It often presented poor performance if the cost was reduced，which could not meet the requirements of reducing cost and increasing efficiency of oilfield. Aiming at the problems，the nanotechnology was introduced into low-density cement slurry. The nanometer material X with size 20—70 nm which composed of silicon，calcium and other elements was modified by polycarboxylic acid surface modifier. Lightening and strengthening material LEM with high water demand was prepared by the combination of material mainly composed of silicon oxide and hollow microsphere. The performance of low-density cement slurry （ 1.30 — 1.50 g/cm³）prepared by modified nanometer material X，LEM，cement，fluid loss additive，retarder and water was studied，and field application was carried out in Shengli oilfield. The results showed that the modified nanometer material X was able to obviously improve the stability of cement slurry and enhance the strength of cement stone. The nanometer low-density cement slurry could resist high pressure，whose density difference could be controlled within 0.05 g/cm³ after exerting pressure to 60 MPa. The nanometer low-density cement slurry with high water cement ratio was able to keep excellent stability and high strength. What is more，it relieved the contradiction between cost and performance of normal low-density cement slurry. The nanometer low-density cement slurry presented low cost and well comprehensive performance and had been successfully applied in Shengli oilfield.