A floating valve providing a parent-and-subsidiary flow-guided floating valve of low pressure drop, high throughput and highly flexible operation maintaining high efficiency within a wide range of gaseous load changes is disclosed. Furthermore, a parent-and-subsidiary flow-guided floating valve having at least two legs, 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 to the overflow cofferdam along the direction in which the liquid flows is also provided.