The invention discloses a physical foaming method for directly forming a foamed product in a mold. Colloidal particles of an elastomer or colloidal particles of a polyolefin composition are adopted asa raw material. The physical foaming method comprises the following steps: (1) if the raw material is the olloidal particles of the polyolefin composition, carrying out a crosslinking reaction on theraw material, and if the raw material is the colloidal particles of the elastomer, implementing a step (2) directly; (2) putting the raw material into a mold with a through hole, putting the mold into a pressure kettle, carrying out high-pressure infiltration by using a supercutical fluid in the pressure kettle, and infiltrating the raw material with the supercutical fluid through the through hole of the mold so as to obtain a half finished product infiltrated with the supercutical fluid; and (3) releasing the pressure of the pressure kettle, foaming the half finished product in the mold directly in a ratio of 1:1, thereby obtaining a finished product of the foam product. By adopting the physical foaming method, supercutical fluid high-pressure infiltration and foaming processes are sequentially implemented in the mold directly, the half finished product does not need to be transferred, and technical effects that process difficulties are reduced and production efficiency is improved can be simultaneously achieved.