Lai 87 oilfield is located in the middle fractured zone in Dong Ying Sag belonged to Ji Yang Downwarp. The oilfield was first use polymer drilling fluid to construct which lead to some complicated problem such as difficult to control theology behavior，blockage during tripping and wellbore collapsing. After treating-agent was carefully selected，and drilling fluid system was optimized in laboratory，high inhibitive ability and anti-caving drilling fluid was developed. The new drilling fluid was field application in 5 wells，and the applications showed that wellbore was stable and no down-hole troublesome condition occurred during the course of drilling wells. At last，the speed of power drill was significantly improved，satisfied the requirements of this well drilling and accelerated the speed of exploration.