The invention discloses a full-open type hydraulic control flap gate and a using method thereof. The full-open type hydraulic control flap gate comprises a dam body, a bottom watertight rubber, a gate leaf support, a gate leaf shaft, a large support rod shaft, a large support rod, a piston rod shaft, a small support rod shaft, a small support rod, a gate leaf hinged support, a gate leaf hinged support shaft, a gate leaf, a hydraulic cylinder, a support seat, a buffer rubber gasket, a side watertight rubber, a cylinder shaft and a hydraulic system. The gate and the method thereof are suitable for storing and draining water of a dam. Water storage, opening and closing of the gate are completely controlled by the hydraulic system, the large support rod and the small support rod support the gate when the gate is closed, thus the hydraulic cylinder is avoided being stressed for a long time, the gate can be completely opened so that the water flow reaches the maximum value, various defects of the traditional flap gate are overcome, the opening and closing accuracy is remarkably improved, no shaking phenomenon exists, the gate can not generate beating and floating phenomena, and the hydraulic system can realize the remote real-time monitoring. One full-open type hydraulic control flap gate can be used and a plurality of full-open type hydraulic control flap gates can also be simultaneously used, and the full-open type hydraulic control flap gate has the advantages of simple structure, low cost and remarkable technical advantages.