The invention discloses a blade self-replacement device of a wind driven generator set, comprising a winding device and a centering device, wherein the winding device comprises a lifting mechanism and a steel wire rope; one end of the steel wire rope is connected with the winding device, while the other end rounds a guide pulley arranged on a cabin framework, a fixed pulley arranged outside a hub, a moving pulley and a fixed pulley arranged in the hub and is finally fixed on the moving pulley; and the centering device is arranged at the root part of an impeller and used for assisting the impeller to connect with the hub. The invention also discloses a working method of the blade self-replacement device of the wind driven generator set. The blade self-replacement device of the wind driven generator set can be used for replacing the impeller by utilizing the configuration of the wind driven generator set per se, better solves the problems caused by the demand of external tools and effectively reduces the maintenance cost of the wind driven generator set.