The invention relates to an urban river sewage interception box culvert sewage disposal and diversion system and method. The system comprises a sewage interception box culvert gate, the upstream of the branch flow end of the sewage interception box culvert is provided with a riverway for connecting a branch flow and a main stream; a box culvert water level meter and a box culvert flow meter are arranged on the upstream of the sewage interception box culvert end of the sewage interception box culvert gate, a dissolved oxygen meter is arranged on the upstream of a river inlet gate of the branchflow, a regulation and storage fork connected with a regulation and storage pool is arranged on the upstream of the dissolved oxygen meter, and a branch flow water level meter and a branch flow meterare arranged on the upstream of the regulation and storage pool gate of the branch flow. A regulation and storage water level meter is arranged in the regulation and storage fork. The water body pollution condition is judged by detecting the dissolved oxygen concentration of the water body, and whether the sewage interception box culvert overflows or not is judged by measuring the depth and the flow of the water body. The opening degrees of gates of the branch inflow trunk stream, the sewage interception box culvert and the regulation and storage pool are selectively adjusted, and the flows from the branch flow to the trunk stream riverway, the sewage interception box culvert and the regulation and storage tank are controlled, so that clean water is ensured to enter the trunk stream riverway, overflow of the sewage interception box culvert is prevented, and overload operation of sewage treatment is prevented.