The invention discloses a method for preparing a large-specification TC4 titanium alloy cast ingot through high-proportion defective titanium materials. The method comprises the steps that 1, the block-shaped and sheet defective TC4 materials are tied into defective material electrodes; 2, the defective material electrodes are welded and cleaned; 3, the cleaned defective material electrodes are smelted to obtain an intermediate cast ingot; 4, the intermediate cast ingot is subjected to one heating number forging, and a long-strip-shaped electrode is obtained and subjected to coping and pickling; 5, the long-strip-shaped electrode subjected to pickling and a sponge titanium electrode block are assembled and welded, and a consumable electrode is obtained and cleaned; and 6, the cleaned consumable electrode is smelted, and the TC4 titanium alloy cast ingot is obtained. According to the method, through reasonable material distribution and multiple times of vacuum consumable electric arc smelting, the large-specification TC4 titanium alloy cast ingot is obtained, the adding proportion of the defective TC4 titanium materials is increased, the content nonuniformity of the defective TC4 titanium materials is reduced, the cleanliness of the TC4 cast ingot is ensured, and the yield and the production efficiency of the TC4 cast ingot are improved.