Abstract: Ocean drilling usually adopts open-circuit drilling without riser, and the main wall protection method is casing. The conventional casing running method has complicated operating procedures and long construction time. The casing is often not in place due to bore shrinkage and collapse, which brings great challenges to the construction. In this paper, the key technology of drill in casing in Ocean Drilling Program is sorted out in detail. This technology uses special supporting tools to realize the “combination of drilling and casing running procedures”, which simplifies the operating procedures and significantly reduces the construction period and solves the technical problems such as the difficulty and high risk of casing running in complex formations by open-circuit drilling in ocean drilling, and provides safety guarantee for deep coring in ocean drilling.