The present invention discloses a self-locking mechanism for use in a drill chuck, comprising: clutch tooth sleeves, fixedly connected with the chuck body of the drill chuck and forming teeth; an oval deformation ring, having a substantially circular first shape and a substantially oval second shape, wherein the oval deformation ring has teeth on the side wall, with the teeth engaging with the teeth of the clutch tooth sleeve when the oval deformation ring is in the second shape; and a control sleeve, for controlling the conversion of the oval deformation sleeve between the first shape and the second shape. The present invention also discloses a force increasing self-locking drill chuck with said self-locking mechanism. The self-locking mechanism according to the present invention can be used in drill chucks of multiple structures, and provides a brand-new thought for the designs of the self-locking mechanisms of drill chucks.