Triassic formations in the west of Middle Tarim Oilfield contain much of purple red shale and brown shale with serious hydration, which cause PDC bit hailing frequently. Taken the well ZG 151 for an example, calculated is the shale content in the strata by using well logging date inverse algorithm, assessed are the shale expansibility and dispersion and measured is the content of strong water sensitivity minerals in the shale by using experiment. The major reasons of bit balling in Triassic formation of well ZG 151 include high shale content of formation, strong water absorption, expansibility and dispersion of the rock shale, high content of strong water sensitivity minerals which cause serious hydration in Triassic shale rock, not timely adding drilling fluid cleaner into drilling fluid, large length of open hole section which causes wellbore soak in drilling mud for a long time. Targeted solutions are proposed in order to prevent bit hailing. Research results show that inhibitive ability improvement of drilling fluid is the main way of preventing hit balling and correct use of drilling fluid cleaner and guarantee of complete cleaning in bottom hole are also very necessary.