The invention discloses an online dynamic balance correction method of a large-size draught fan impeller, belonging to the field of equipment overhauling, and aiming at reducing impeller assembling and disassembling procedures and shortening an overhauling period. The online dynamic balance correction method comprises the following steps: A, connecting one end of a vibration detection balancing apparatus with a driving end of the draught fan impeller on line and connecting the other end of the vibration detection balancing apparatus with a driven end of the draught fan impeller; marking a vibration starting phase point on a wheel disc of the impeller; B, starting the vibration detection balancing apparatus and detecting an original vibration amplitude and an original phase of a bearing bush at the driving end of the draught fan impeller; C, calculating balance counter weight needing to be added and a phase of the added balance counter weight; and D, adding the balance counter weight to the back surface of the impeller. According to the online dynamic balance correction method of the large-size draught fan impeller, after the balance counter weight and the mounting position of the balance counter weight are measured in a large-size draught fan installation site by utilizing the vibration detection balancing apparatus, the balance counter weight is mounted on the impeller and the draught fan impeller does not need to be assembled and disassembled, so that the impeller assembling and disassembling procedures are reduced and the overhauling period is shortened.