The invention discloses a preparation method for a leather fatting agent, and belongs to the technical field of preparation for leather fatting agents. The method includes the steps that leaf fat is weighed, diced and stewed, and oil residues are collected; barium nitrate and water are calcinated to obtain nanometer barium oxide powder; butyl titanate, absolute ethyl alcohol, glacial acetic acid and other substances are mixed, subjected to vacuum drying and roasted to obtain nanometer titanium dioxide powder; and the oil residues, the nanometer barium oxide powder and the nanometer titanium dioxide powder are mixed according to a proportion, roasted and subjected to ultrasonic dispersion, then silicon powder and talcum powder are added to be roasted, pig gastric juice and peanut oil are dropwise added during roasting, after heat preservation, distilled water is added, the solid content is controlled, and the leather fatting agent is obtained after mixing. The preparation method has the beneficial effects that the preparation steps are simple, the obtained product can be emulsified easily and is good in affinity with leather, and the problem that acid resistant stability, permeability and lubrication performance are poor is effectively solved; and after the leather fatting agent is used, the hardness and ductility of the leather are effectively improved, and the leather is prevented from being hardened and fractured.