Provided is a process for directly producing sulfur trioxide and sulfuric acid from gypsum. Sulfur trioxide is directly substituted with silicon dioxide by thermal or light-quantum activation, which is assisted with catalytic activation, while restraining reducing atmosphere and removing the resultant sulfur trioxide in time. The resultant sulfur trioxide is then used as raw material to produce sulfuric acid by a well-known method in prior art. The process has the advantages of simplified operational steps, little investment, low energy consumption and manufacturing cost, and low environmental pollution.