The invention discloses a hydropower station gate and a gate closing method. The hydropower station gate comprises a water flow through opening, a fixed foundation and an arc gate, wherein a support component is mounted on the arc gate; an articulation base is mounted on the fixed foundation; the support component is articulated with a semicircular disk which is also articulated with the articulation base; the upper part of the arc gate is articulated with a first lifting rod; the semicircular disk is also articulated with a second lifting rod; a first lifting device and a second lifting device are mounted on the fixed foundation; the upper end of the first lifting rod is connected with the first lifting device; the upper end of the second lifting rod is connected with the second lifting device; a circle of elastic rubber is also arranged on the outer side of the arc gate; a liquid injection cavity is formed in the elastic rubber; an oil inlet pipe and an oil outlet pipe are also mounted in the arc gate. According to the device disclosed by the invention, liquid can be injected into the elastic rubber through a hydraulic pump, and the elastic rubber expands and blocks the inner surface of the water flow through opening to realize a sealing effect.