The invention discloses a rotating device used before hoisting of a wind power main shaft flange without occupying travelling crane. A rack is included; a flange conveying device is arranged on the work face of the rack; one end of the rack in the conveying direction is provided with a rising and falling type limiting baffle; a flange rising and falling mechanism is further included, and is arranged on the two sides of the flange conveying device and located below a flange; the flange lifting mechanism is provided with a rotating driving mechanism driving the flange to rotate; and a flange storing frame provided with a flange storing table is further included, and is internally provided with a lifting mechanism driving the flange storing table to rise and fall. By means of the rotating device used before hoisting of the wind power main shaft flange without occupying the travelling crane, manual operation for installing hole alignment before hoisting of flanges is reduced, the labor intensity of workers is relieved, efficiency is high, and safety is extremely good; and in the hole alignment process, the flanges do not make contact with the lower conveying device, and the service life of the lower conveying device is prolonged.