A constructing-and-forging method for preparing homogenized forged pieces comprises: preparing preformed billets: cutting off a plurality of continuous casting billets, milling and smoothing surfaces of the billets to be welded, performing vacuum plasma cleaning operation to the surfaces to be welded, stacking the plurality of billets and sealing around the surfaces in a vacuum chamber by electron beam welding; forge-welding and homogenizing the preformed billets: heating the preformed billets to a certain temperature in a heating furnace and taking the heated preformed billets out of the heating furnace, forging the preformed billets by a hydraulic press, then using three-dimensional forging to disperse the welded surfaces such that composition, structure and inclusion of the interface areas are at the same level as those of the bodies of the billets. Cheap continuous casting billets are stacked and forge welded.