Positioning non-return structure for knife rest

The utility model relates to a positioning non-return structure for a knife rest. The positioning non-return structure comprises a base, a positioning sleeve and a positioning pin, the base is connected with a machine tool; the positioning sleeve is rotationally connected with the base around the own axis; the positioning sleeve is provided with a plurality of positioning grooves, and the positioning grooves are distributed in the circumferential direction of the positioning sleeve. The two side walls, distributed in the circumferential direction of the positioning sleeve, of the positioning groove are provided with a positioning face and a disengaging face correspondingly. The positioning surface is parallel to or coincides with the axis of the positioning sleeve; an acute angle is formed between the separating surface and the positioning surface, and an opening of the acute angle deviates from the positioning sleeve; the positioning pin is slidably connected with the base along the axis of the positioning p