The invention discloses a quenching device for uniformly cooling workpieces by adjusting the flow velocity. The quenching device comprises a quenching cooling tank body and a quenching medium, whereinthe quenching cooling tank body comprises an outer tank and an inner tank; devices for stirring the quenching medium are arranged on the periphery of the inner tank; the bottom of the inner tank is provided with annular drainage covers comprising annular horizontal drainage plates and annular upward drainage plates; the upward drainage plates in the annular drainage covers are arranged concentrically, and the tops of the upward drainage plates are located in the same horizontal plane; the horizontal drainage plates in the annular drainage covers correspond to outlets of flow guide tubes and are parallel to the bottoms of the inner tank, and the horizontal drainage plate corresponding to the outer annular upward drainage plate is located on the upper layer, and the upward drainage plate located in the center is overlapped with the bottom of the inner tank.