The invention relates to an input end for yawing gearboxes and pitch-varying gearboxes. The input end comprises a box body, a sun wheel shaft and a seal ring; a combined friction pair containing fixed friction plates and movable friction plates is arranged between the box body and the sun wheel shaft; the sun wheel shaft is provided with a pressing piston; a check ring, an elastic check ring for holes and an annular gasket are arranged in the box body, the annular gasket abuts against the box body, the pressing piston and the annular gasket are located on the two sides of the friction pair respectively, and the pressing piston is limited in the box body; a shifting fork is arranged in the box body, the front end of a fork head of the shifting fork is a wedge-shaped side, a push-pull rod of the shifting fork is provided with an upper spherical ring groove and a lower spherical ring groove and is in butt joint with the fork head after one end of the push-pull rod is inserted into the box body, and the upper spherical ring groove or the lower spherical ring groove of the push-pull rod is located in the box body when the push-pull rod drives the fork head to move; after a shifting fork ring groove in the pressing piston penetrates through the check ring, the inner wall of the shifting fork ring groove and the moving track of the end of the fork head of the shifting fork are orthogonal, and when the fork head is inserted into the shifting fork ring groove, the wedge-shaped side at the front end of the fork head drives the inner wall of the shifting fork ring groove and drives the pressing piston to move axially along the sun wheel shaft.