Wet flue gas desulfurization (FGD) systems that remove sulfur dioxide (SO2) from in flue gas, a cause of acid rain, operate at many power plants, but problems remain to be solved concerning the detailed behavior of these systems. Here, we experimentally studied the behaviors of O-2 and CO2, which have not been fully clarified, and conducted Simulations using Models based on the present experimental results for O-2 and CO2 and results reported for other chemical models. From the experimental results, we obtained an equation For O-2 absorption as a function of superficial gas velocity, and one for CO2 desorption as a function of superficial gas velocity, pH and temperature for the oxidation tank in an FGD system. We also conducted simulations for FGD systems based on the typical chemical behaviors observed experimentally. First, we calculated the distributions of flue gas concentration, pH, and the solid phase absorbent concentration for two typical FGD methods, the limestone-gypsum method (LGM) and magnesium hydroxide method (MHM), and Studied the differences in behavior between them. Next, we studied the optimum values of water depth in the oxidation tank and gas flow rate of the air compressor for oxidation and got the values of 6 m for the former, and of 2,500 m(3) (STP).h(-1) (LGM); 2,700 m(3) (STP).h(-1) (MHM) for the latter.