The invention relates to a sealing mechanism for a guide shaft of a wind power gearbox, which is high in sealing performance, safety and reliability. The sealing mechanism comprises a guide shaft main body (1) with a length of greater than 1m, a guide shaft upwind end cover (2) comprising a connection part (21) and an end cover body (20) radially extending outwards from the left end of the connection part (21), a planetary carrier (3), a guide shaft sleeve (4), a guide shaft downwind end cover (5) comprising a cover body (50) and an assembly part (51) axially stretching out to the left from the cover body (50), a second-stage input shaft end cover (6), two O-shaped sealing rings (11) and a bearing (12). The sealing mechanism is characterized in that the left end of the guide shaft main body (1) is fixedly assembled into the inner hole of the connection part (21) of the guide shaft upwind end cover (2); and one of the two O-shaped sealing rings (11) is installed between the right end surface of the end cover body (20) of the guide shaft upwind end cover (2) and the left end surface of the planetary carrier (3).