The invention relates to an auxiliary device, in particular to an auxiliary device for replacing baby diapers. The technical problem to be solved is to provide the auxiliary device for replacing the baby diapers, wherein people can replace the baby diapers more conveniently, and the situation can be avoided that movement of infants affects the replacement of the baby diapers. According to the technical scheme, the auxiliary device for replacing the baby diapers includes an n-shaped base, a pillow, a u-shaped plate, a movable plate, a torsion spring, a swing plate, an inversely L-shaped rod andthe like. The right side of the top of the n-shaped base is provided with a pillow, the upper portion of the left side face outside the n-shaped base is hinged with the u-shaped plate, the middle ofthe right side face inside the u-shaped plate is hinged with the movable plate, and the torsion spring is arranged at the hinge portion of the movable plate and the u-shaped plate. An infant sits on the n-shaped base, the two legs of the infant can swing upwards by pulling a slide sleeve, the baby diapers are placed on the swing plate and the movable plate, the baby diapers can cover the ass of the infant by pulling the swing plate, people do not need to lift the two legs of the infant, and the baby diapers are more convenient to replace.