The invention discloses a flood flow-increasing drainage concrete manhole cover, the structure includes: a flood aid and drainage device, a water inlet, a support bar and a fixing frame, wherein the flood aid and drainage device comprises a flushing hole, a manhole cover main body, a compression spring, a deflector, a supporting float, a micro force piston, water collection holes, a buoyancy drainage tanks, a push rod, a buoyancy deflector and a clamping block. A slight force piston is nested in that flushing hole, the inner surface of the well cover main body is in contact with the outer surface of the supporting floating plate. The beneficial effects are: in case of heavy rain or sustained rainfall in the city, under the action of the flushing hole and the water collecting hole, when theinternal water level rises, the supporting floating plate floats upward, so that people do not step into the well by mistake, and under the action of the diversion platform, the water generates eddycurrent state, finally forms siphon effect, improves the drainage speed, avoids the flood caused by heavy rain in the city, and causes the phenomenon of slow drainage after the water accumulates in the city.