The CGSD01 well, as a 4000m deep geothermal survey well deployed by CGS , is of great significance to the evaluation of deep geothermal resources in Dongli Lake District, Tianjin. The quality requirement on the well completion is high. The Institute of Exploration Techniques, CAGA, while testing of the drill rig XD40 developed under the research program “4000m Geological Core Drilling Technology and Equipment”, innovatively set the first tier casing of 3397mm to1467m by use of the buoyancyassisted casing setting process with the less hook load of the drill rig, laying a good foundation for upcoming drilling operations. This paper introduces the theoretical analysis and practical application of setting casing with buoyancy.