Reversing structure of middle speed reducer of helicopter

The invention provides a reversing structure of a middle speed reducer of a helicopter. A middle speed reduction input gear assembly comprises a middle speed reduction input gear and a middle speed reduction input shaft fixed to the middle speed reduction input gear, and a middle speed reduction output gear assembly comprises a middle speed reduction output gear and a middle speed reduction output shaft fixed to the middle speed reduction output gear; and straight lines on which the medium-reduction input gear and the medium-reduction output gear are positioned intersect and are arranged at an acute angle. The straight line where the medium-reduction input shaft is located intersects with the straight line where the medium-reduction output shaft is located and forms an acute angle, so that the input gear and the output gear are opposite in rotating direction, namely the medium-reduction input shaft and the medium-reduction output shaft are opposite in rotating direction in the course of the helicopter. The mi