The invention relates to a flat float type float valve mounted on a instant heating type waterer water-level control water tank for controlling the water level in the water tank, comprising a valve body, a valve flap, a lever, a cone sealing gasket and a flat float, wherein an excurrent ostium is set on the valve body and the cone sealing gasket for sealing the excurrent ostium is set before the excurrent ostium and fixed on the valve flap and the valve flap is hinged with the lever; a guide stub pipe for guiding the movement of the valve flap is set on the valve body; the flat float is of flat shape and a tie bar extending downwards is set on the flat float; one end of the lever is hinged with the lower end of the tie bar and the distance between the hinge center and the hinge axle center of the lever balance pivot is a and the distance between the hinge axle center of the hinge part of the valve flap and the lever and the hinge axle center of the level balance pivot is b and the ratio of a to be is not more than 3; a bearer is set on the valve and the level uses the bearer to obtain the pivot.