Abstract: Because of its deeply embeded, complexity of geologic constructure, coexistence of defferent pressure layers, and so on, there are a lot of severity accident of well bore instability such as collapsing, lost circulation, hinderong and blocking in the formations of Triassic and Carboniferous in Tahe Oilfield. The mechanism of well bore instability was made clear through X-ray diffraction, Scanning Electron Microscope, swelling, shale dispersion, specific surface area and specific water wet amount of shale, analysised the mineral, stratum or stucture and physi-chemical performance on representative shale cones. The effective well bore stability technic-countermeasure were brought for ward, and 2 kinds of anti-sloughing drilling fluids were selected on this bases. The site trial indicate that the 2 kinds of anti-sloughing drilling fluids roll it’s hoop when be transfered in midway, simple in manage and maintenance, and effective in anti-collapsing, quickened the drilling velocity and saved integrated drilling cost.