The present invention discloses a method for preparing nano-copper powder, comprising: (1) providing a dispersion solution, containing copper salt precursor and disperser, the disperser is dissoluble in both water and weak solvents, and is an acrylic modified polyurethane disperser; (2) providing a reducer dispersion solution, containing reducer, the reducer is organic borane; (3) contacting the reducer dispersion solution with the dispersion solution in a condition enough to reduce the copper salt precursor by the reducer into elementary copper; (4) separating copper nano-particles from reaction solution obtained by step (3), and drying separated copper nano-particles by spray drying, so as to obtain the nano-copper powder. The nano-copper powder prepared by the method in accordance with the present invention is dispersible in both water and environment-friendly weak solvents, which can be used to prepare weak solvent-type electrically conductive ink.