The invention discloses a drilling fluid capable of protecting a coal bed methane reservoir. The drilling fluid comprises the following ingredients in percentage by weight: 100 parts of fresh water, 0.1-0.3 part of pH value modifier, 0.5-10 parts of water-sensitivity inhibitor, and 0.1-1 part of waterproof blocking agent. For the drilling fluid, the density is 1.01-1.08g/cm<3>, the pH value ranges 8 to 10, the expansion rate reduction ratio is greater than or equal to 60%, the contact angle reduction rate is greater than or equal to 50%, the hygroscopic-state recovery rate of the core permeability is greater than or equal to 85%, the dry-state recovery rate is greater than or equal to 95%, the coal powder landberra volume reduction rate is greater than or equal to 15%, clay-free phase does not exist, the damage to the coal bed methane reservoir caused by same-phase invasion can be furthest reduced, the hydration of the clay mineral in coal petrography can be effectively prevented, water blocking is reduced, the coal bed methane can be forced to be desorbed from the surface of the coal petrography, the coal bed methane reservoir can be effectively protected, the stability of the coal bed well wall can be retained, the practicability is strong, and the stronger popularization and application values can be achieved.