The invention discloses an automatic hydraulic control leaping weir initial rainwater catch basin and a flow closure method. The automatic hydraulic control leaping weir initial rainwater catch basin and the flow closure method are suitable for the improvement of a bypass flow rainwater pipeline. The catch basin comprises a catch basin body, a flow inlet pipe, a water closure pipe, an automatic hydraulic control weir body, four limiting blocks, a floating cylinder, sector flow side baffles, flow discharging small holes, a separation wall, an overflowing pipe, a manhole, steps, a weir plate shaft and the like. The flow closure method is conducted by the catch basin and when it rains, flow of the water inlet pipe is enlarged along with the enlargement of rainfall. When the flow of the water inlet pipe is enlarged to a certain degree, a flow-jetting outer curve crosses the automatic control weir. According to the automatic control weir, a weir plate is opened under the buoyancy of the floating cylinder and the water flow in the flow inlet pipe is completely abandoned until the amount of the water flow of the flow inlet pipe is nearly zero. Due to the flow discharging action of the flow discharging small holes, the floating cylinder descends, the weir plate is reset, and clean rainwater can enter a water receiving body at the later period. The catch basin is completely controlled through hydraulic power, other control devices are not needed, operation is stable, maintenance is simple, and management is convenient.