With the deepening of exploration and development, the completion depth of the ultra-deep well during the final stage cementation has exceeded 7400m. The complex geological structure and variety of borehole structures bring many quality control difficulties for cementing. Liner cementing has the characteristics of “two highs, one small and one low”, that is, high risk of leakage, high working pressure, small displacement of slurry and low displacement efficiency, leading to incomplete displacement of slurry during cementing. Through a field case of application of cementing technology in Shunbei Oilfield, this paper investigates the method to improve the cementing quality under the condition of incomplete displacement, so as to improve the cementing quality in this block and increase the service life of oil wells.