The invention relates to a method for plating a Ni-P alloy on an additive-manufactured aluminum alloy surface, and belongs to the technical field of surface modification. The method comprises the following steps: performing a sand blasting process, an alkaline oil-removal process and an acid-corrosion stripping pretreatment process on a plated part; plating zinc on the surface of the plated part;and plating a nickel alloy on the plated part. Compared with a surface treatment process for casting workpieces, the method has the advantages of stably and uniformly plating a 3D printed molded partby improving a plated part pretreatment process, changing components and content of alkaline liquor and controlling components and content thereof in nickel plating liquor, greatly reducing surface roughness of the 3D printed formed part, and improving corrosion resistance, wear resistance, weldability and electric contact performance of the 3D printed formed part.