The invention relates to a dual-drainage flapper type drainage mechanism. The dual-drainage flapper type drainage mechanism comprises a drainage valve, a wrench component and a flapper. The drainage valve comprises a valve barrel and a counterweight barrel, wherein the valve barrel sleeves the counterweight barrel, and the counterweight barrel drops to drive the flapper to close. During drainage, the flapper is opened, and semi-drainage and full drainage of the drainage mechanism are achieved by controlling the counterweight barrel dropping start speed. The dual-drainage flapper type drainage mechanism has the advantages that the shortcomings of a pulling dual-drainage flapper type drainage valve in the prior art are overcome, semi-drainage and full drainage are controlled by controlling negative pressure of the counterweight barrel, and the drainage mechanism is simple in integral structure, small in size, high in universal matching performance, good in sealability, convenient to assemble by users, stable in water level after drainage and the like; drainage quantity can be adjusted at a semi-drainage gear, so that water can be saved more effectively; drainage of the drainage mechanism is controlled by the wrench component, and the semi-drainage gear and a full drainage gear can be achieved by one wrench; a lifting rod which can be easily replaced can facilitate maintenance, and accordingly, the drainage mechanism is simple to operate.