The invention relates to a floating box type weir gate and an application method thereof. The floating box type weir gate is arranged between a main channel and a auxiliarychannel for draining water in the main channel to the auxiliary channel, and comprises a weir gate and a floating box chamber, wherein a floating box is arranged in the floating box chamber, and is connected with the weir gate through a rotating shaft; the floating box is fixed to the rotating shaft through a floating box support arm; the weir gate is fixed to the rotating shaft through the weir gate support arm; and the floating box and the weir gate are positioned on two sides of the rotating shaft correspondingly. The floating box type weir gate has the beneficial effect of simple structure, reasonable design, capability of fully using the mechanical principle to open and close the weir gate, reliable operation performance, high automation degree and lower maintenance cost.