The invention discloses a surface modification method of superfine diamond micro-powder. The surface modification method includes the steps of firstly, mixing superfine diamond micro-powder and a dispersing agent solution, performing solid-liquid separation, and filtering to remove impurities; secondly, drying the superfine diamond micro-powder wet material obtained in the first step through a flow drying manner to obtain surface-modified superfine diamond micro-powder. The surface-modified superfine diamond micro-powder is stale in dispersion in a water system, applicable to the polishing of high-end precise products such as semiconductors and optical lenses, high in polishing efficiency, good in polishing quality, free of scratches after polishing, capable of avoiding damage of a to-be-polished workpiece and capable of satisfying the requirements of the current technical field of the high-end precise products.