The invention discloses a preparation method of zinc caseinate. The preparation method comprises the steps: dissolving zinc salt which is insoluble in water in an alkaline solution, adding a prepared zinc salt solution in milk casein as a raw material, and puffing through an extruding machine to produce the zinc caseinate. The zinc caseinate prepared by using ammonia water or a sodium hydroxide solution as a zinc oxide dissolution solution is lower in ash content, high in chelating zinc content, relatively high in viscosity, and relatively good in emulsifying property; meanwhile, the problems of complicated manual operation, such as raw material dissolution, acid precipitation, colloid milling, converting, and spray-drying, in procedures and energy consumption in the prior art are solved. According to the zinc caseinate, the content of zinc protein is not less than 88 percent, the content of fat is not more than 2.0 percent, the content of ash is not more than 5.5 percent, the content of zinc is not less than 1.6 percent, the contents of all physicochemical indexes accord with the standard, the content of the zinc is within a standard range; the zinc caseinate has the relatively good viscosity, relatively good color and normal smell, and is simple in process and small in energy consumption.