The invention relates to a thermoplastic polyurethane modified composite material for FDM (frequency division multiplexing) 3D printing and a preparation method thereof. The composite material is prepared from the following components in parts by weight: 70-95 parts of thermoplastic polyurethane, 1-5 parts of antioxidant, 1-5 parts of hydrolysis-resistant stabilizer, 1-5 parts of compatilizer, 1-5 parts of lubricant and 1-10 parts of other assistant. Compared with the prior art, the antioxidant, hydrolysis-resistant stabilizer, lubricant and other assistants are added, so that the modified composite material has the advantages of favorable mechanical properties, high elasticity, favorable wear resistance, higher heat stability, hydrolysis resistance, higher oxidation resistance and higher processability. When being used for FDM 3D printing, the thermoplastic polyurethane modified composite material has the characteristics of smooth printing process, no odor, smooth printing product surface, beautiful appearance, stable size, low tendency to shrinkage, favorable mechanical properties, high flexibility, high heat stability, high hydrolysis resistance, high oxidation resistance and high processability.