The catalytic oxidation of SOP on polyacrylonitrile-based active hollow carbon fiber (AHCF) was investigated. A single-pass reacting system was developed to study this reaction. The sulfur dioxide contained in the gas stream was oxidized to sulfuric acid in the presence of oxygen and water. Four types of active hollow carbon fibers were prepared through various conditions in order to study the influence of the structure of AHCF on the characteristics of the catalytic oxidation. The fiber sample with more mesopores and micropores showed a higher degree of reaction, but the degree of reaction declined after a period of time, possibly due to the saturation of the active sites by the reaction products. The degree of reaction from the fiber sample with fewer mesopores and micropores did not show the overshoot and reached a steady state after a period of time.