This paper reports a study on the simultaneous removal characteristics of SO3 in a wet flue gas desulfurization (WFGD) system. The impacts of the operating parameters, including liquid-to-gas (L/G) ratio, inlet SO3 concentration, flue gas temperature, superficial velocity, and slurry temperature, on the SO3 removal efficiency and SO3 aerosol characteristic were studied. Results showed that the overall SO3 removal efficiency varied from 20% to 55% under the experimental conditions. For the SO3 aerosol, particles measuring <0.1 mu m and >0.5 mu m had a higher removal efficiency, whereas particles measuring 0.1-0.5 pm were relatively difficult to remove in the WFGD system. Increases in L/G ratio and SO3 concentration exerted positive effects on the SO3 aerosol capture, whereas superficial velocity, flue gas temperature, and slurry temperature had negative effects. After installing a sieve plate, the SO3 removal efficiency increased from 49.88% and 53.46% to 51.77% and 58.05%, respectively, under two typical conditions. A multilayer perceptron artificial neural network model was applied to evaluate the relative importance of each parameter in SO3 removal performance. Results showed that inlet flue gas temperature, inlet SO3 concentration, and slurry temperature had a relatively strong impact on SO3 removal performance.