This invention relates to the core component of a floating valve tray-floating valve. The objective is to provide a parent-and-subsidiary flow-guided floating valve of low pressure drop, high throughput and highly flexible operation that can maintain high efficiency within a wide range of gaseous load changes. The technical proposal is: a parent-and-subsidiary flow-guided floating valve, wherein the body of the parent valve is a symmetrical plane figure with the central axis line as the symmetrical line, the central axis line points to the overflow cofferdam along the direction in which the liquid flows and there are at least 2 legs below the body of the parent valve. The front leg is longer than the rear leg so that when the parent valve is fully open, a 2-10 degree angle opens between the body of the parent valve and the valve orifice toward the overflow cofferdam. On the body of the parent valve is a parent valve hole, on which is the subsidiary valve, which is a movable valve smaller than the parent valve in terms of area with its circumference parallel to that of the parent valve. There are at least 2 legs under the body of the subsidiary valve and the front leg is equal to or longer than the rear leg so that when the subsidiary valve is fully open, a 0-10 degree angle opens between the body of the subsidiary valve and the body of the parent valve toward the overflow cofferdam.