Abstract: The geological characteristics of Pingdingshan coal field and the general aspects of well-wall protection are introduced briefly. The composition features, performance parameters and recipes of five kinds of dilling fluid are mentioned in detail. The densities,contents of solids,viscosities,rheological and filtrating properties of the various kinds of drilling fluid are discussed. The main technical function and mechanism of the drilling fluid in prevention of percolating and flowing out of water are also studied. The drilling effects and economic benefits of different kinds of drilling fluid are summarized.