A forming method for modular metal construction comprising the following steps: preparing 2 N prefabricated blanks, N≥2; the prefabricated blanks are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare 2 N-1 level I hourglass-shaped modules; performing upsetting deformation along the height direction and inter-forging heat preservation after heating the level I hourglass-shaped modules to prepare intermediate blanks, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks; the intermediate blanks prepared in the step are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare 2 N-2 level II hourglass-shaped modules, and performing upsetting deformation along the height direction and inter-forging heat preservation after heating the level II hourglass-shaped modules, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks; if 2 N-2 is more than 1, the intermediate blanks prepared in the step are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare multilevel hourglass-shaped modules, performing upsetting deformation along the height direction and inter-forging heat preservation after heating the multilevel hourglass-shape modules, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks, and repeating the step once or for multiple times until one blank is prepared; processing the blank into a component or a part. preparing 2 N prefabricated blanks, N≥2; the prefabricated blanks are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare 2 N-1 level I hourglass-shaped modules; performing upsetting deformation along the height direction and inter-forging heat preservation after heating the level I hourglass-shaped modules to prepare intermediate blanks, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks; the intermediate blanks prepared in the step are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare 2 N-2 level II hourglass-shaped modules, and performing upsetting deformation along the height direction and inter-forging heat preservation after heating the level II hourglass-shaped modules, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks; if 2 N-2 is more than 1, the intermediate blanks prepared in the step are made into frustum-shaped units, the small surfaces of the two frustum-shaped units are stacked together and vacuum electron beam welding is conducted to prepare multilevel hourglass-shaped modules, performing upsetting deformation along the height direction and inter-forging heat preservation after heating the multilevel hourglass-shape modules, the height reduction of implementing upsetting deformation on the hourglass-shaped modules is equal to 30 to 55 percent of the total height of the blanks, and repeating the step once or for multiple times until one blank is prepared; processing the blank into a component or a part.