Abstract: The cementing casing of large diameter well has large outer diameter and mass, and is lowered by welding connection. The special specification, size and connection mode require the casing to adopt special technology. Through-hole tools and lifting tools are processed separately according to casing specifications; the core of the method includes the development of the buoyancy plug and the casing anti-extrusion control. The buoyancy plug enables mud buoyancy to ensure that the rig is able to lower the mass casing with little lift while facilitating subsequent cementing; in the process of using mud buoyancy, anti-extrusion control ensures that the empty section of casing does not collapse under mud pressure in the well. It has been proved by practice that the key technology of large diameter casing can be handled well to ensure safe casing running without damage.