The invention discloses a tail water treatment device for a sewage plant and rural domestic wastewater. The tail water treatment device is characterized by comprising a dosing device and a partition reactor, wherein the dosing device comprises a dosing tank and a dosing pump; the partition reactor is divided into a partition coagulation region, a reaction region, a settling region and a clarification region; six partitions and a water inlet are arranged in the partition coagulation region; the reaction region is connected with the partition coagulation region, the settling region and the clarification region; a sludge hopper is arranged in the settling region; a sewage discharging opening is formed in the left side of the sludge hopper; a water outlet is formed in the clarification region;the height of the water outlet is equal to that of the second partition. The tail water treatment device disclosed by the invention occupies a small area, is low in capital construction cost and lowin energy consumption, greatly reduces the tail water treatment cost of the sewage plant and the rural domestic wastewater, and is suitable for treating tail water of the sewage plant and the rural domestic wastewater.