The invention discloses a preparation method of a hot phase-change heat-insulating material. The preparation method comprises the following steps of mixing paraffine with stearic acid so as to obtain a mixture; heating the mixture so that the mixture dissolves; then adding illegal cooking oil, and performing stirring so that the dissolved mixture and the illegal cooking oil are sufficiently and uniformly mixed; performing cooling to the room temperature so as to obtain impregnant; and then performing vacuum impregnation on the impregnant in waste cotton products so as to obtain the hot phase-change heat-insulating material. The hot phase-change heat-insulating material prepared from the waste cotton products and the illegal cooking oil has good thermal insulating properties; when the hot phase-change heat-insulating material is used as the heat-insulating material of the winter plastic shed, the problem of high cost of planting of the winter shed is effectively solved, besides, the waste cotton products and the illegal cooking oil are also recycled, and the hot phase-change heat-insulating material has extremely important significance in realization of recycling of recourses, saving of effective energy sources and environmental protection.