The interface of an electrolyte and cathode strongly determines the oxygen reduction reaction and cell stability, but it is susceptible to sulfur impurities like SO2 in air. In this study, a 3D solid oxide fuel cell model is developed based on experimental characterization to reveal sulfur-deactivating active cathodes. The results indicate that both the average values for electric and ionic current densities drastically decrease after sulfur poisoning; meanwhile, their distributions are also changed, suggesting that the involved oxygen reduction reaction is detrimentally affected. Moreover, the temperature decreases after poisoning due to electrochemical reaction slowdown near the interface of the active cathode and electrolyte. The pronounced temperature changes together with differences in the thermal expansion coefficient of neighboring components, further resulting in uneven stress distributions at the active cathode, possibly bringing out cracks and bending. Thermal stresses are reduced after sulfur poisoning, especially for the third principal stress, which produces a decrement of 154 MPa. The visualized results of the current density, temperature, and stresses are helpful to understand the sulfur poisoning behavior and also to better understand the internal changes of some crucial electrochemical processes beneficial for further optimization of the microstructural stability.