The invention relates to a depolymerization and grading process method of a nanodiamond aggregate, which mainly comprises the following process steps: 1) synchronously carrying out mechanical grinding and chemical modification on the nanodiamond, dispersing the nanodiamond into small aggregates with the average particle size of 7-200 nm, and 2) removing coarse nanodiamond and other components in the suspension; 3) adding a wetting agent, a surfactant, a dispersion stabilizer, and a pH value regulator, and dispersing the diamond by adopting ultrasonic or (and) stirring; 4) grading the nanodiamond; the particle diameter of the composite material can be controllably adjusted between 7 and 200 nanometers, and the composite material can be widely applied to the fields of composite plating, (chemical mechanical) ultra-precise polishing, running-in (lubricating) oil, additives of wear-resistant materials and the like. The Nano diamond suspension that adopts the method of the present invention to make even particle size distribution and dispersion stabilization is fabulous, can deposit within 6 to 12 months, and tangible sedimentation does not occur. After the cross-flow classification technique provided by the invention classification, particle size distribution narrows down, and the technical stability of the product increases substantially. When utilizing ZETASIZER3000HS to carry out granularity Detection, its average grain diameter is 7 to 200nm, and the absolute value of the superficial electrokinetic potential of Nanodiamond can be controlled in more than 35mv. Technical field: the invention belongs to the manufacturing field of Nanodiamonds; its application relates to Ultraprecise polished, the compound plating of the workpiece of artificial lens, the break-in oil of engine, and the areas such as enhancement of material. Background technology: the reason that the suspension of Nano diamond in water is brutal for stable existence is mainly that the surface of Nano diamond can be very high. To reduce the energy of the system, it often reaches a steady state between particles by drawing close mutually, also have, the particle is thinner, the distance between the particle is shorter, Van der Waals force between the particle impels them to reunite, in addition, effects such as the hydrogen bond on Nano diamond surface, the wet bridge of absorption also can cause the coalescent of particle, the direct coalescent result is that the second particle diameter becomes big. Sedimentation takes place and causes the instability of the system. If you are looking for high quality, high purity and cost-effective Diamond Nanoparticles, or if you require the latest price of Diamond Nanoparticles, please feel free to email contact mis-asia.