The invention relates to the molding technology of nonmetal composite materials, and provides a method for preparing large-scale composite-material aerogenerator blades; the method mainly relates to the following steps: preparing an upper and a lower housing of the blade; directly laying a crossbeam (3) in the blade housing body when laying the blade housing; completing the preparation of the blade housing by an integral forming process of the crossbeam (3) and the blade housing; during vacuum perfusion, setting different rapid diversion zones and flow obstruction zones (7) according to the change of the permeation rate of a resin in fibers so as to allow the resin to infiltrate the whole laid layer more rapidly and much better; laying a diversion net on the upper surface of the laid blade housing; setting a certain interval between diversion media for the arrangement of the obstruction zones (7), and laying a flow obstruction belt (9) on the diversion media where flow obstruction is needed; or directly laying the flow obstruction belt on the upper surface of the blade housing; adding continuous strand mats into the interior part of the crossbeam layer so as to accelerate the permeation rate of the resin in the layer.