A drill chuck, comprising: 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 outer socket in a driving manner; characterized by the drill chuck further comprising: 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 the locking plate, and the locking balls are movably arranged along the slide grooves, the locking mechanism further comprising an annular pad located between the locking balls and the nut and movably arranged along an axial direction of the drill body, an inner wall of the annular pad having a plurality of limit surfaces cooperating with the inclined guiding holes respectively, so that the annular pad is incapable of rotating around the drill body. 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 outer socket in a driving manner; characterized by the drill chuck further comprising: 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 the locking plate, and the locking balls are movably arranged along the slide grooves, the locking mechanism further comprising an annular pad located between the locking balls and the nut and movably arranged along an axial direction of the drill body, an inner wall of the annular pad having a plurality of limit surfaces cooperating with the inclined guiding holes respectively, so that the annular pad is incapable of rotating around the drill body. 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 the locking plate, and the locking balls are movably arranged along the slide grooves, the locking mechanism further comprising an annular pad located between the locking balls and the nut and movably arranged along an axial direction of the drill body, an inner wall of the annular pad having a plurality of limit surfaces cooperating with the inclined guiding holes respectively, so that the annular pad is incapable of rotating around the drill body.