The invention discloses an automatic distributor and a distributing method. The automatic distributor comprises a mixing and stirring tank (1), wherein the mixing and stirring tank (1) is communicated with a material tank (3) through a material pipe (2); the mixing and stirring tank (1) is communicated with n reagent tanks (5) through n reagent pipes (4); the mixing and stirring tank (1) is communicated with a pure water source through a water pipe (6); a liquid level meter is arranged on the mixing and stirring tank (1); a discharging tube (7) is arranged at the bottom of the mixing and stirring tank (1); a motor (10) is arranged on the top of the mixing and stirring tank (1) and drives a stirrer (11) in the mixing and stirring tank (1); flow meters, feeding pumps and pipe valves are arranged on the material pipe (2) and the n reagent pipes (4). By the automatic distributor, dependence on persons and labor intensity in the sanding process of high-purity ultra-fine active aluminum powder are reduced, efficiency is improved, costs are reduced, and the purity of the product is kept.