The invention discloses a preparation method of nickel nano particles. The method comprises the following steps of: in nitrogen atmosphere, adding nickel chloride into absolute ethyl alcohol, then adding [BMIN]BF4 ionic liquid as dispersant, thus obtaining nickel source dispersion solution; adding hydrazine hydrate solution with the volume concentration of 20%-25% into the nickel source dispersion solution while stirring until generating black precipitate, continuously stirring for 1-2 hours, thus obtaining reaction liquid; centrifuging, taking out the precipitate and repeatedly washing the same by the deionized water, thus finally obtaining precipitate with little anhydrous ethanol and placing into a vacuum drying box; standing in the vacuum drying box for 24-48 hours at the pressure of 10-100Pa and the temperature of 80-90 DEG C to remove moisture and anhydrous ethanol in the precipitate, thus obtaining the finished products of nickel nano particles. The nickel nano particles produced by using the method is good in dispersibility, simple in used equipment, easy to master operating conditions, meanwhile, free of high-temperature roasting in the preparation process, saving in energy and lowered in cost.