The invention discloses an inflating device for blowing off water droplet. The inflating device comprises an inflating flange, an inner shell, an inflating pipe, an outer shell, an inflating gasket and an inflating end cover, wherein one end of the inflating flange is butted and tightened with a cooling box behind a quenching treatment section through a screw, while the other end is butted and welded with the outer shell; the inner shell is arranged in the inflating flange; one end of the inner shell is pressed against an inner step of the inflating flange, while the other end is arranged in the outer shell; the end face of the inner shell is connected with the inflating gasket which is arranged between the outer shell and the inflating end cover; and the inflating end cover is fastened to the outer shell through a screw. The inflating device is simple in design and easy to implement, and can blow off large droplets carried by a steel bar and damage a steam blanket enclosing the surface of the steel bar, so that the cooling speed is improved, and the formed scale attached to the surface of the steel bar during quenching-heating can be damaged.