The invention provides a segment-by-segment forming method for a large curved surface adopting a discrete die. A large 3D curved-surface part is difficult in forming, and in a conventional integral stamping forming method, a large die is needed, large or extra-large table facet machining equipment is required, and therefore, the production cost of large 3D curved-surface parts is extremely high. According to the invention, a set of discrete profile adjustable die is adopted, a to-be-formed large curved surface is sequentially divided into a plurality of segments with size equal to that of the forming area of the die; during forming of each segment, the discrete die is divided into an effective forming area and a forming transition area; and by reasonably designing the profile shape of the die of the forming transition area, deformation of joint part of adjacent forming segments are in uniform transition, so as to avoid production of forming defects, and the large curved-surface part is finally obtained after segment-by-segment forming. The method disclosed by the invention only needs one set of discrete die, and with small equipment, large-size parts can be formed, and quick machining of large curved-surface parts with low cost can be achieved.