A drill chuck comprises: a drill body having a plurality of inclined guiding holes distributed evenly along a circumferential direction; a plurality of clamping jaws arranged slidably in the inclined guiding holes respectively and having external thread segments; an outer socket rotatably fitted over the drill body; and a nut engaged with the clamping jaws and connected to the out socket in a driving manner; further comprises: a locking mechanism located between a first thrust surface of the drill body and the nut and having a locking plate and locking balls, wherein an end face of the locking plate facing the nut is thereon provided with a plurality of slide grooves having a helix angle, the helix angle of the slide grooves is less than a friction angle between the locking balls and locking plate, and the locking balls are movably arranged along the slide grooves.