The invention relates to the technical field of tamponade liquid for well completion and cementation, in particular to tamponade liquid for well completion and cementation and a preparation method thereof. The tamponade liquid for well completion and cementation is prepared from, by weight, 1.0-3.0 parts of carboxymethylcellulose, 0.5-1.5 parts of sulfonated tannin, 0.5-1.0 part of xanthan gum, 0.2-0.5 part of sodium gluconate, 0.3-0.6 part of tartaric acid and 100 parts of water. The tamponade liquid for well completion and cementation is good in stability at the high temperature of 80 DEG C to 120 DEG C, and has certain viscosity and shearing force, meanwhile, the phenomenon of high-temperature viscosity reduction or high-temperature thickening is avoided in the well cementation coagulating waiting process, an electrical logging cannot meet resistance, and the solid phase suspension need of drilling fluid with barite as main weighting materials on site can be met.