Powder metallurgy is important in material preparation. Due to the inertness of carbon materials, however, sintering powdered carbon into physically coherent bulks has been a great challenge even at a high temperature (2000 ℃). Improving the sintering activity of carbon powders is the key to the success of the consolidation of the carbon powders. Here ordered mesoporous carbon (OMC) is used as the starting material to produce highly homogeneous novel carbon bulks. During sintering at 1800 ℃, the huge specific surface area of the OMC greatly promotes the migration of carbon atoms and thus the sintering of the OMC by surface diffusion mechanism. When nanodiamond (ND) is added, the volume expansion associated with the phase transformation of diamond to graphite facilitates the densification of the powder compacts. The strong connection between the OMC and the graphite onions derived from the ND bestows the as-prepared carbon bulks with excellent mechanical properties. The current research pioneers a novel way to prepare high-strength carbon materials at relatively low temperatures.