The invention discloses a polymer nano-modified nylon 11 composite material and a preparation method thereof. The polymer nano-modified nylon 11 composite material comprises the following components in parts by weight: 50-80 parts of nylon 11, 20-30 parts of starch, 20-40 parts of polylactic acid, 5-10 parts of methyl methacrylate, 1-6 parts of maleic anhydride, 1-3 parts of oxalic acid, 1-4 parts of triphenyl phosphite, 2-8 parts of nanosilicon dioxide, 2-6 parts of nano calcium carbonate, 0.1-0.8 part of stearate, 0.1-0.6 part of borate, 1-5 parts of trimethyl chloro propane trimethyl acrylate and 1-3 parts of an antioxidant. The preparation process is simple, feasible, and easy to process; and the prepared polymer nano-modified nylon 11 composite material has the advantages of a polymer, a nano material and nylon 11, and is good in low-temperature toughness, good in barrier property, low in cost and suitable for the industries such as automobiles, aviation and electrons.