The invention relates to a drilling fluid used for active mud shale drilling, and the drilling fluid is used in oilfield drilling. The drilling fluid comprises the following components in percentages by weight: 2-6% of bentonite, 0.2-0.5% of coated inhibitor, 0.2-1.0% of flow pattern regulator, 0.2-0.5% of high-temperature-resistant polymer filtrate reducer, 4-7% of potassium chloride, 1-3% of polymeric alcohol, 0.5-1.0% of polyamine inhibitor, 0.5-1.0% of anti-balling fast drilling agent and 45-85% of water. The drilling fluid has the inhibition property and lubricating property approximate to that of an oil-based drilling fluid, solves the problems that the mud making of the mud shale is severe, mud escapes from a vibrating screen, the viscous shearing of the drilling fluid increases and the rheological properties of the drilling fluid deteriorates during strong-mud-making active mud shale drilling, prevents destabilization of the active mud shale, dispersion of drill cuttings, balling of drill bit, and adhesion and coalescence of the mud shale, and increases the drilling speed of the active mud shale.