The invention relates to a drilling fluid for improving the mudstone drilling speed. The drilling fluid is prepared from the following components by weight: 1000 parts of water, 10-30 parts of bentonite, 0.5-1.5 parts of sodium carbonate, 2-20 parts of a flow pattern regulator, 2-15 parts of a fast drilling agent, 2-8 parts of polyether amine, 1-6 parts of a polymer coating agent, 2-15 parts of a salt-tolerant and temperature resistant filtrate reducer, 20-35 parts of sulfonated phenolic resin and optionally 15-35 parts of an plugging agent. The accelerating drilling fluid provided by the invention has excellent resistance to salt, calcium and bad soil, and can effectively improve the rate of penetration. The invention also relates to a preparation method of the drilling fluid. The method includes the steps of: adding bentonite and sodium carbonate into water, mixing the substances evenly, then conducting standing maintenance, then adding the polymer flow pattern regulator, the polymer coating agent, the fast drilling agent, polyether amine, the salt-tolerant and temperature resistant filtrate reducer, sulfonated phenolic resin and the plugging agent, mixing the substances evenly, and performing standing for standby use. The invention also relates to application of the accelerating drilling fluid.