The invention discloses a polyurethane-imide-base multifunctional composite damping material and a preparation method thereof. The preparation method comprises the following steps: 1) mixing dibasic alcohol, pyromellitic dianhydride, a catalyst and a filler to obtain a mixture; sequentially adding diisocyanate and a chain extender into the mixture, and mixing to obtain a thermoplastic polyurethane imide composite material; 2) curing the thermoplastic polyurethane imide composite material, and pressing into a sheet; and 3) radiating the sheet to obtain the polyurethane-imide-base multifunctional composite damping material. The thermoplastic PUI (polyurethane imide) used as the base and the reactive flame retardant tetrabromo ether are subjected to radiation crosslinking to obtain the multifunctional composite damping material with heat-insulating property, bullet-proof performance, shielding property and flame retardancy. The preparation method is simpler, and is convenient to operate and beneficial to large-scale production.