The invention discloses a structure for selecting a rotation angle by a shifting fork for a worm gear-worm reducer. The structure comprises a base, a complete-tooth worm gear, an incomplete-tooth worm gear, a worm and the shifting fork, wherein the complete-tooth worm gear and the incomplete-tooth worm gear are respectively connected to a shaft I and a shaft II; the shaft I and the shaft II are both mounted on the base via bearings; the tail end of the worm is connected to the shifting fork; the initial end of the worm is arranged between the complete-tooth worm gear and the incomplete-tooth worm gear; the complete-tooth worm gear and the incomplete-tooth worm gear are symmetrically distributed at two sides of the worm; and the shifting fork is arranged on a sliding groove and moves upwards and downwards under the action of a driving mechanism. According to the invention, the complete-tooth worm gear and the incomplete-tooth worm gear are both arranged on the worm gear-worm reducer, and the adopted shifting fork moves upwards and downwards to enable the worm to choose to be meshed with any one of the complete-tooth worm gear and the incomplete-tooth worm gear, so that the change of the rotation angle of the worm gear-worm reducer is realized, and the universality is good; and a difference between the complete-tooth worm gear and the incomplete-tooth worm gear is that whether a stopping sheet exists, so that the cost input is low.