In view of the defects with the conventional casing running process with the cement buoyancy plug for coal mine large diameter wells， such as multiple steps， drilling fluid pollution， high amount of concrete settlement and residuals， research was carried out on the casing running process with the steel buoyancy plug in the case of a large diameter gas extraction well at a coal mine in Huozhou . This paper introduces the process principle， calculation of critical casing strength at elastic buckling deformation and material yield failure， the structure and assembly design and strength calibration for the steel buoyancy plug. This process was used to run gas extraction casing of 150t at ?836 mm diameter， and the field use has proven that this technique can reduce tripping of the drilling string during casing running operation， shorten the operation time， and eliminate concrete residue in casing； in addition， the process is feature of simple manufacture and convenient operation. It can provide experience and reference for future similar projects.