In this article, preparation of nano-graphite powders in a steel chamber by using pure TNT (trinitrotoluene) explosives has been reported. X-ray diffraction results indicated that the black solid powders which were collected from the wall and the bottom of the chamber after detonation have the graphite structure and the average size of the particles of the graphite is 1.86-2.58 nm. Transmission electron microscopy confirms that the black powder is hexagonal-graphite structure with ball or ball-like shape. The grain size of the nano-graphite measured by small angle x-ray scattering lies in the range of 1-50 nm, 92.6wt% of the powder particles is smaller than 16 nm and the average diameter of the grains is 8.7 nm. Specific surface area of the nano-graphite is about 500-650 m2/g. Using nano-graphite as carbon source and choosing Fe powders as the catalyst, the ball-like and lumpy diamonds of 5-15 μm have been synthesized under high-temperature and high-pressure conditions of 1250-1330 K and 5.1 GPa. The synthesized temperature is about 300 K lower than that of bulk graphite synthetic diamond.