Fine Cu powder was prepared by a solid-liquid plasma discharge electrolysis process using a CuSO4 - H2SO4 solution. The X-ray diffraction results indicated the presence of Cu2O impurity in the obtained Cu powder. The Cu content in the powder increased with increase in the concentration of CuSO4, and pure ultra-fine Cu powder was obtained using 0.2 M CuSO4 - 0.2 M H2SO4 solution. Emission spectrum analyses indicated that a large number of hydrogen radicals (H center dot) generated in solution contained H2SO4 during the process of plasma discharge was the reason for the formation of pure Cu, therefore the formation mechanism of Cu could be described by the whole reaction Cu2+ + 2H center dot -> Cu + 2H(+), and the formation of impurity Cu2O was caused by the reaction of Cu-2(OH)(2)(2+) + 2e(-) -> Cu2O + H2O in electrolyte. The formation process of Cu and Cu2O in two types of solution were described in detail. Scanning electron microscopy analyses indicated that Cu2O particles were polyhedron-shaped with an average diameter of 100-200 nm. (C) 2018 The Electrochemical Society.