It is very difficult in the coalfield drilling process because rather complex strata are usually encountered; such as breaking layer, collapsing layer and hydration expansive layer. Heavy density and low filtration drilling fluid system were developed with antisloughing, inhibiting and proper density. Field application proves that the drilling fluid system can perfectly maintain borehole stability and effectively inhibit the hydration expansion of mud stone and shale with the accident rate in wireline coring drilling decreased.