The present invention discloses a process for producing nanometer powders, comprising the following steps: (a) providing reactant solution A and reactant solution B that can rapidly react to form precipitate; (b) continuously adding said solution A and solution B into a mixing and reacting precipitator with a stator and a rotor in operation, respectively; and (c) post-treating the precipitate-containing slurry discharged continuously from the mixing and reacting precipitator. The present process could produce nanometer powders with adjustable particle size, good homogeneity in size and good dispersity. The method also has the characteristics of high production yield, simplicity in process and low consumption of energy. It could be applied to produce various nanometer powders of metals, oxides, hydroxides, salts, phosphides and sulfides as well as organic compounds.