The invention relates to a tail gas treatment device and a tail gas treatment method. The tail gas treatment device comprises an air inlet, a gas flow channel, a first water jet hole, a wastewater tank, an air outlet, a water quality detection unit, a water outlet and a water return port. The gas flow channel is communicated with the air inlet. The first water jet hole is used for jetting water to tail gas in the gas flow channel; the wastewater tank is used for accommodating the wastewater generated after treatment of the tail gas; the air outlet is communicated with the gas flow channel, and is located at the tail end of the gas flow channel; the water quality detection unit is used for detecting whether the wastewater in the wastewater tank meets the recovery requirements; the water outlet is used for discharging the wastewater in the wastewater tank when the quality of water in the wastewater tank does not meet the recovery requirements; the water return port is connected to the first water jet hole through a water return pipeline, and is used for inputting the water from the wastewater tank to the first water jet hole through the water return pipeline when the quality of water in the wastewater tank meets the recovery requirements. The tail gas treatment device provided by the invention can realize reuse of wastewater.