In the oil and gas pre-exploration in northern part of Datong basin, the construction area formation is interbedded mainly with mudstone, sandy mudstone, carbonaceous mudstone and sandy conglomerate, loose cemented gravel in upper part, which are broken with block falling, and mudstone has strong water sensitivity and is easy to disperse and mud making, wall protection is difficult, blocking and sticking occur in drilling process. The designed well depth is generally 1000～3000m, different types and structures of drill bit, tools and coring tool are adopted, drilling parameters are adjusted. Dual polymer filming non-solid drilling fluid system is selected together with corresponding technological process and measures to realize wall stability and the side tracking are successfully completed.