The invention discloses a preparation method of copper nanoparticles with different particle diameters and relates to a metal nanoparticle. The invention provides a preparation method of copper nanoparticles with different particle diameters, which has simple, economic, environment-friendly process. The preparation method comprises the following steps: adding metal salt of copper chloride or copper acetate, a solvent, a protective agent, a complexing agent and a surfactant in a vessel in sequence, and stirring to obtain a mixture, wherein the protective agent is polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, or the like, the complexing agent is oleic acid, hexadecylamine, oleamide, or the like, and the surfactant is hexadecyl dimethyl ammonium bromide, sodium dodecyl benzene sulfonate or the like; adding a reducing agent in the mixture for reacting, wherein the reducing agent is ascorbic acid, sodium formaldehyde sulphoxylate, sodium borohydride, or the like; cooling the reactant till the temperature is below 40 DEG C, then adding a precipitating agent, mixing, and centrifugally separating; then washing with the organic solvent, centrifugating, and extracting the precipitate; and then drying the precipitate to obtain red powder copper nanoparticles with different particle diameters.