The extended reach horizontal wells (horizontal to vertical ratio greater than 2) are characterized by large deviation, poor hole quality, low casing central degree and low cement displacement efficiency, which makes it difficult to guarantee the cementing quality. To solve these above problems, a three-dimensional cementing displacement calculation model is established. The effects of casing central degree, slurry rheology, displacement and irregular wellbore diameter on cementing displacement efficiency are analyzed. The extended reach horizontal well cementing technology is formed to ensure the displacement efficiency. The results show that increasing the casing central degree and displacement could effectively reduce the drilling fluid attached to the wellbore wall and improve the cementing displacement efficiency. The cementing displacement efficiency could be improved by reducing the consistency of the spacer, properly increasing the cement consistency coefficient K in addition of the fluidity index n ≥ 0.8. The displacement dead zone could be formed in the irregular diameter section, which lead to the reduction of displacement efficiency. The reduction of the diameter expansion ratio and the increase of the length of the diameter expansion section will improve the displacement efficiency. The above research results have been successfully applied in Chenghai extended reach horizontal well A. The application effect is good, and the qualified rate of cementing quality is more than 80%. It could effectively improve the cementing displacement efficiency and guarantee the cementing quality of extended reach horizontal wells, which could provide reference for similar extended reach horizontal wells.