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The particle size distribution of copper powder produced by the domestic electrolysis method is generally above 30 μm, and most of the copper powder obtained is concentrated in the low-end and low-end fields with low added value, which cannot meet the higher requirements of the electronic information field. This paper uses chemical-electrochemical synergistic reaction to prepare electronic grade ultrafine copper powder, and discusses the influence of chemical reaction time, current density and cathode composition on the particle size, morphology and structure of copper powder. The results showed that with the extension of the chemical reaction time, the particle size of the copper powder gradually increased, and the dendritic shape gradually became dense; with the increase of the current density, the particle size gradually decreased, showing a well-dispersed dendritic shape. The optimal process conditions are determined as follows: the chemical reaction time is 1 min, the current density is 300 A.m_^-2, and the aluminum alloy cathode plate. Under this process, a dendritic ultrafine copper powder with an average particle size of 6.44 μm, a bulk density of 0.828 g.cm_^-3 and good dispersibility can be obtained. It is further proved that the chemical-electrochemical coordinated reaction mechanism is that the substitution reaction generates crystal nuclei in advance, and electrochemical deposition grows in situ on the crystal nucleus to form dendritic crystals.