In the top fill cementing process in karst strata with large leakage, the cement slurry is easy to be diluted due to the displacement fluid or changes in the stable liquid level. If it happens during the injection of the displacement fluid, cementing will fail; and if it happens after the injection, the cement slurry may not rise to the annulus of the overlapping casing or be diluted without forming the cement plug due to many factors. This paper summarizes the key technology of the top fill cementing process in view of the setting location of the drill string, and changes in the stable liquid level during and after slurry water injection. Based on the field cases, some artificial control methods are proposed to improve the success rate of cementing.