Abstract: Wangnangou Block has been one of the focuses for exploration and development in Ansai oilfield for recent years, yet cementing quality in this area is poor. Causes of interfering the zonal isolation are investigated, e.g., water-oil layers and bottom water reservoirs exist in the production zone, associated gas in the crude oil, and formation pressure imbalance, etc. According to these conditions, cement additive GJR of early strength and fluid loss controlling is added into the cement slurry so as to obtain such properties as early strength, minimal inflation and thixotropic behavior. This technology has been used in over 300 wells, and remarkable improvement on cementing quality has been achieved.