The invention discloses a preparation method of hollow @ double-layer sludge carbon. The preparation method comprises the following steps: taking a low-density spherical foam material which is thermally decomposed easily as a sacrificial hard template, wrapping the surface of the spherical foam material with sludge containing an enhancer, drying, preforming into spherical foam @ sludge as a precursor, wrapping the surface of the precursor with sludge containing different pore-forming agents, drying, and performing high-temperature thermal decomposition under an anaerobic condition, wherein the hard template is decomposed and a hollow is left, the sludge in the inner layer is thermally decomposed and carbonized to form a firm composite supporting material, and the sludge in the outer layer is activated during thermal decomposition and carbonization to form the multi-stage porous hollow@ double-layer sludge carbon. With the preparation method, the hollow double-layer sludge carbon is prepared from sludge and other wastes through two-step preforming and thermally decomposing, so that the problem of environment pollution of the sludge is solved, and the prepared formed sludge carbon material has the characteristics of low density, firm structure, large specific surface area and the like, can be used as an adsorbent, a biological filler, a catalyst carrier and the like, can use waste to treat waste, and is a high-added value multifunctional environmental material.