The invention discloses an overflow-circulation classification method for diamond micro-powder, belongs to the technical field of diamond production, and solves the defects of low production efficiency, large particle size distribution and high impurity content in the prior art. The overflow-circulation classification method for the diamond micro-powder comprises the following steps: (1) setting a water pressure and a flow rate of an overflow, and carrying out constant-pressure water supply by a constant-pressure water supply system; (2) carrying out overflow classification for the diamond micro-powder by an overflow classification system; and (3) carrying out precipitation classification by a precipitation water storage system to obtain the diamond micro-powder with the needed particle sizes. The method disclosed by the invention has high production efficiency and less interference of human factors; and the produced diamond micro-powder are centralized in distribution, uniform in particle sizes, and low in impurity content.