Anti-overflow valve for toilet seat

A anti-overflow valve for toilet seat arranged between a down water gap and a downcast pipe includes a valve body; a plurality of inner reinforced plates for supporting, integrated connecting with inner wall of the valve body; a floating ball disposed between the plurality of inner reinforced plates; and a seal ring equiped between lower edge of the toilet seat and upper edges of the plurality of inner reinforced plates to form the down water gap. In normal times, sewage is drained from space between the down water gap, the floating ball and the inner reinforced plates, while the downcast pipe is blocked, sewage upbears the floating ball to float upwards, and seals up the above down water gap to prevent the sewage overflow to outside.