Zhoushen Well X1 is a deep and exploration well, there are some difficulties in drilling fluids treating: The borehole is large, the open hole is long and the rock density proportion is high in the overlying strata. So the drilling fluids must have good suspended and sand carrying; there are brown mudstone, gypsum mudstone and light gray fine sandstone in the lower strata, swelling and hole shrinkage always happen. So the key point is ensuring well wall stability and preventing swelling and hole shrinkage. The drilling fluids must have strong Calcium-tolerance and good compatibility with formation for coping the swelling and hole shrinkage of the high conductivity mudstone in the deep well section. Because well temperature is high in the lower section, the stability of anti-high temperature is very important. The drilling fluids must have prevention against high temperature denseness ability and good rheological property.