Cretaceous gravel layer, multilayer goaf and mud stone formation have been difficult for coalfield geological drilling. Firstly, it is easy to collapse due to the loose cementation at upper sand gravel layer hole section; secondly, strong water sensitivity, high swelling, joint and fissure development easily cause hole shrinkage, mud making and different degrees of leakage at lower hole section; thirdly, the wall protection in multilayer goaf. In view of the above, in the complex formation drilling in Datong coalfield, potassium ammonium polymer low solid mud is selected by repeated tests. The practice proves that the accidents of hole collapse, block falling, hole shrinkage can be prevented by using potassium ammonium polymer low solid mud to improve drilling efficiency and reduce cost.