The invention discloses a recombinant human interleukin-12 preparation for injection and a preparation method thereof, and aims to provide a preparation which has the advantages of good stability and low moisture content. The invention has the technical point that each milliliter of preparation contains 2.5-10mu g of recombinant human interleukin-12, 50mg of filling agent, 5-20mg of freeze-dried protective agent, 2.30mg of disodium hydrogen phosphate, 0.52mg of sodium dihydrogen phosphate and 7.02mg of sodium chloride. The preparation method comprises the following steps of: (1) weighing disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium chloride according to the formula proportions, adding water for injection, stirring for dissolving, regulating the pH value to 6.8-7.8 with sodium hydroxide or hydrochloric acid, and metering the volume to the formula proportion; (2) taking out the solution, adding the formula proportion of the filling agent, stirring for dissolving, then adding the formula proportions of the freeze-dried protective agent and recombinant human interleukin-12, stirring until the materials are uniform, carrying out sterile filtration, and respectively packaging in bottles of 1ml; and (3) freeze-drying. The invention belongs to the technical field of medicine preparation.