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The authors studied the low-density slurry system��because the fracture pressure of some strata in cementing was low��the well walls could not bear the high pressure by slurry columns��leading to the leak of slurry and the cement return height could not reach engineering designation in Wuqi oilfield�� Through the laboratory experiment�� the lightening materials of fly ash��floating bead and the composit system of both were analyzed and the proper mixture ratio was decided�� In order to improve the intensity of low-density cement��the enhanced stabilizer was added into low-density system�� The experimental and practiced results showed that preparing the low-density slurry with lightening materials and decreasing the pressure of slurry column were the efficient ways to cement return height of slurry cementing in weak formations��which played positive roles to enhance the quality and prolonged the life of well cementing��