Abstract Hole wall's stability is a complex problem which exploration engineering has been working to solve. There are many reasons which may lead to hole wall's instability. Aiming at hole wall's stability in coal exploration, this paper takes shale as objects of study and uses the MPC method (for example: analyzing on rock's microstructure characteristics, physical and mechanical properties, and chemical characteristics) to make a thorough research on unstable coal shale formations in a work area in LuoPing district. The results show that the shale in the area has high content of the mixed-layer of illite and smectite, water intrusion dramatically decreases rock strength and elastic modulus and leads to poor mechanical properties. Considering the coupling effects of mechanical properties as well as the drilling fluid sealing characteristics of drilling fluid must be improved and its osmotic pressure should be reduced.