A triple eccentric valve with a symmetric drain-proof ring includes a valve body, a stem, a valve disk, a waterproof washer, and a drain-proof ring. The valve disk is formed as an asymmetric conical shape. The drain-proof ring is an O ring and is arranged in a stepped recess of the valve disk to seal the waterproof washer; the drain-proof ring is symmetric to the axis of the ring. In assembly state, a periphery of the drain-proof ring resists against an inner wall of the annular seat. The drain-proof ring is symmetrical. Furthermore, an inner side or a part of the valve seat has a shape matched to a sweeping track of an outermost point of the drain-proof ring so that when the drain-proof ring moves along the valve seat, only force tangent to the inner side of the valve seat is applied from the drain-proof ring to the valve seat.