The invention relates to a self-locking engaging and disengaging gear for a cutter of a mixing cup. The engaging and disengaging gear comprises a gear-box and a mixing cutter, and is characterized in that one end of the mixing cutter is connected with the gear-box by a drive connection head and the other end thereof is rotatably arranged on the mixing cup, wherein a first cavity is arranged in the mixing cutter, a slide bar connected with a spring is arranged in the first cavity, a locking bar is arranged in the slide bar, one end of the locking bar is connected with the mixing cup, and an engaging and disengaging mechanism is arranged between the slide bar and the locking bar; and a push bar on the drive connection head extends into the first cavity and is connected with one end of the slide bar. The mixing cutter comprises a cutter body and cutter blades arranged thereon, wherein a first cavity is arranged in the cutter body, positioning holes communicated with the first cavity are arranged on one end of the cutter body, an opening is arranged on the other end of the cutter body, and more than one positioning blocks are arranged on the peripheries of the positioning holes. The invention is characterized by simple and reasonable structure, high safety, and low vibration and noise.