The invention discloses a poly epsilon-caprolactone/poly (beta-hydroxybutyrate-valerate) blend membrane and a preparation method thereof, and belongs to the field of biodegradable materials. The blend membrane is a membrane produced by irradiation modification by an electron beam produced by gamma rays or an electron accelerator, the irradiation dose is 2-70 kGy, the membrane thickness is 20 to 200 microns, and taking the total membrane mass as 100%, the PCL (polycaprolactone) content is 20-80%, and the PHBV (poly hydroxyl butyrate valerate) content is 20-80%. The preparation method is as follows: respectively dissolving PCL and PHBV in solvents to obtain a solution 1 and a solution 2; (2) mixing the solution 1 and the 2 solution to obtain a mixed solution3; (3) casting a glass plate with the mixed solution3 to make the thickness uniform, forming a membrane by solvent evaporation, and obtaining a blend membrane by vacuum drying to a constant weight; and (4) performing irradiation on the blend membrane. According to the blend membrane, mechanical properties of the PCL and the PHBV are complemented, the brittleness of the PHBV is improved, the degradation performance is adjustable, and the method is simple in process and less in environmental pollution.