Flood control deep tunnel and flood drainage method

The invention provides a flood control deep tunnel. The flood control deep tunnel comprises a vertical shaft and a tunnel body, an isolation plate is arranged on the lower portion of the tunnel body,a sewage cabin is arranged below the isolation plate, a middle-later-period rainwater cabin is arranged above the isolation plate, and the bottom of the vertical shaft communicates with the sewage cabin or the middle-later-period rainwater cabin through a flow dividing mechanism; and a cleaning pipe is arranged in the sewage cabin, a plurality of water spraying holes are formed in the cleaning pipe, the cleaning pipe is connected with a water inlet pipe, the upper end of the water inlet pipe penetrates through the isolation plate and extends into the middle-later-period rainwater cabin, and avalve is arranged at the upper end of the water inlet pipe. The invention further provides a flood drainage method. The tunnel is smaller in occupied area and smaller in construction amount; and automatic cleaning of the sewag