Abstract: Large-hole deep drilling is an inevitable option in the casing program design of medium and deep wells, and its comprehensive drilling fluid technology is one of the key factors for the implementation of large hole.Shallow formation in central Bohai Sea area is easily hydrated and expanded, and cuttings are easily bonded into clusters, so large-hole deep drilling in this area is faced with difficult cuttings carrying, wellbore instability and heavy drilling fluid maintenance.The comprehensive drilling fluid technology used for large-hole deep drilling includes mud ball prevention and control technology, rheological property control technology, wellbore stability technology and sectional fine maintenance process, and it can guarantee the smooth implementation of large-hole deep drilling.