Abstract: Based on the water balance in limestone\|gypsum wet flue gas desulfurization (FGD) system, a mathematical model considering steam and water from flue gas carrier, gypsum and drainage is set up for the calculation of FGD systems water consumption. Taking a typical FGD system in 300MW thermal power unit as an example, its water consumption is calculated, and a further study on the main factors which influence the water consumption is conducted, the results show that the water taken away by the outlet flue gas of FGD absorption tower takes up the main part of the whole water consumption of the FGD system, while the inlet and outlet flue gas temperatures of the FGD absorption tower are the most important factors on the water consumption of the FGD system. A series of optimization proposals for water conservation are proposed consequently.