The present invention relates to preparation of a mono-epoxy-terminated polysiloxane-modified gelatin gradient membrane by a freeze-drying method. Surfactant sodium alkyl sulfate is dissolved in water and formulated into an aqueous solution, the aqueous solution is stirred for 1-2h at 40-60 DEG C under the condition of pH of 8 to 11, gelatin is added, stirring is performed for 4-8h, and mono-epoxy-terminated polysiloxane with the molecular weight of 500 is added to obtain a mono-epoxy-terminated polysiloxane-modified gelatin solution. The mono-epoxy-terminated polysiloxane-modified gelatin solution is centrifuged at a low temperature, after layering, water is added into an intermediate layer for even mixing, ethanol is added, after even mixing, 0.5-0.8ml of the mixture is measured and dropwise added into a gelatin substrate, standing is performed for 12-18h, liquid nitrogen is used for freezing, and the freeze-drying method is used for drying to obtain the mono-epoxy-terminated polysiloxane-modified gelatin gradient membrane. The mono-epoxy-terminated polysiloxane-modified gelatin gradient membrane has the characteristics that component concentration change is gradient in longitudinal section, and the mono-epoxy-terminated polysiloxane-modified gelatin gradient membrane is high in tensile strength, good in hydrophobicity and soft, and so on.