The invention provides a flexible interlink steel gate and a support opening/closing device thereof, which belongs to the technical field of hydraulic engineering. The flexible interlink steel gate mainly comprises a flat plate steel gate (1), a gate support hinge (2), a cylindrical rubber bag communicated (7) with a water supply/drainage system, a flange (6) at the upper part of the rubber bag, a connecting piece (8) at the lower part of the rubber bag, a bottom water stop (3), a side water stop (18), a door interlink, and the like. The steel gate is made of a steel panel and a light structural steel beam grid system through welding, adjacent gates can be connected through the water stops and the interlink fasteners, and one gate is connected with a bottom plate pre-embedded part (5) through a hinge, and is controlled to be opened or closed through the expansion and the retraction of the rubber bag which is filled with water or discharges water. The invention has the advantages that less central piers are used, water is not blocked, the gate has a light and thin body and can be controlled to be opened or closed by a person, the water filled and discharge amount is small, the cost of construction is low, and the use is convenient, so that the flexible interlink steel gate and the support opening/closing device thereof can be widely applied in mountainous area watercourses and small hydro-electric power plants.