Abstract: Aiming at the problems such as low construction efficiency and high labor intensity in the process of lowering large diameter casing through the broken stratum of complex roof high level drilling in coal mine, a large diameter casing lowering device is designed. This paper introduces the design of large diameter casing lowering device, describes in detail the design process of front inner support assembly, back inner support assembly, cylinder block, slip and other key parts, and describes the technological steps of casing lowering by drilling rig. During the field industrial test, 68 casings with a diameter of ϕ245 mm and a length of 1.5 m were run in 4 directional boreholes with a tilt angle of 17°, totaling 102 m. The large diameter casing lowering device is sensitive and reliable, and can meet the functional requirements of mechanized large diameter casing lowering in complex roof high level drilling.