The invention discloses a flue gas treatment device, and particularly relates to a device for treating flue gas generated after a wet flue gas desulfurization technology. Specifically, the flue gas treatment device is characterized by comprising a steam compression cycle system of a first heat exchanger, the first heat exchanger is arranged in a flue between a wet desulfurization device and a chimney, and the first heat exchanger is used as a condenser of the steam compression cycle system for heating the flue gas. According to the flue gas treatment device, the lifting height of the flue gas at a chimney outlet is increased, dewing is avoided, gypsum rain is avoided, and environment is well protected; corrosion to the chimney is relieved; operating loads of a cooling tower are reduced, and the generating efficiency of a unit is improved.