The invention discloses a quantitative valve and a working method thereof, and belongs to the field of valves. The quantitative valve comprises a liquid inlet control motor, a valve body, a liquid outlet control motor and an electric telescopic rod; the valve body is provided with a valve body liquid inlet and a valve body liquid outlet; a flange connector is arranged at the valve body liquid inlet, and is used for being connected with a liquid inlet pipeline conveniently; a valve body liquid inlet channel extends downwards from the flange connector to the interior of the valve body; a first notch is formed in the valve body liquid outlet, and the valve body liquid outlet is a liquid inlet of the whole quantitative valve; a valve element is arranged at the upper portion of the interior ofthe valve body, a valve element rod, a valve element liquid inlet and a valve element liquid outlet are arranged on the valve element, and the valve element rod is connected with the electric telescopic rod; the first notch is formed in the valve element liquid outlet, and the valve element liquid outlet of the valve element is a liquid outlet of the whole quantitative valve; and the bottom of theinner side of the valve body is provided with a valve base. According to the quantitative valve and the working method thereof, large-capacity quantification can be realized.