The invention discloses an aftertreatment processing method for waterproof down. The method comprises steps as follows: step 1), down addition: a washed finished down product is added to a down storage box, and down is enabled to pass an iron removing device through quantitative feeding; step 2), spraying: the down is extracted from the down storage box, chemical spraying is performed through thequantitative feeding, and stirring is performed during spraying; step 3), dehumidification and sizing: the down enters a dehumidification stage after being stirred, and excessive water in a spraying device is dried by a fan; step 4), drying: the down is sucked into an oil heat conduction drying device by the fan and is dried through the quantitative feeding; step 5), cooling and dedusting; step 6), secondary cooling; step 7), down discharge and packaging. According to the scheme, the down subjected to waterproof treatment is provided with a protecting nanofilm and has excellent waterproof performance, filling power is improved, and heat retention property of the down is improved; besides, the down has certain dampproof and antibacterial functions, and is protected from breeding bacteria and producing peculiar smell due to dampness.