The invention provides a laser additive manufacturing method applied to a large-sized metal part. The laser additive manufacturing method comprises the following steps: according to the configuration characteristics and load distribution characteristics of the integral structure of the part, dividing the part into a plurality of sub-blocks; according to the shape structure characteristics of all the sub-blocks, separately dividing the sub-blocks into a plurality of scanning areas: wed plate scanning areas, edge strip scanning areas, T-shaped block scanning areas and ear plate scanning areas, and then setting the scanning sequence according to the principle that priority is given to the farthest scanning area; adopting a short-edge reciprocating scanning mode in the scanning areas, guaranteeing the consistent widths of scanning paths in the scanning areas, and completing the manufacturing of all the sub-blocks; assembling, clamping and positioning the manufactured sub-blocks according to the position relation determined when the part is divided into the sub-blocks, guaranteeing that deformation allowance is left at the seam between two adjacent sub-blocks, and adopting a deformation mapping mode for positioning between two adjacent sub-blocks; and subjecting all the positioned sub-blocks to laser additive connection till all the sub-blocks are connected together to form a whole, thereby completing the manufacturing of the part.