According to actual sewage composition in Shanghai area, an artificial sewage of high concentration was prepared as corrosion medium. Corrosion tests were conducted on C35, C50 concrete and its mortars containing fly ash by way of accelerated corrosion of stress corrosion and dry moisture alternating cycle. Testing results show that stress corrosion (deflection) under loading, strength loss, expansion rate and reinforcement bar rust inhibiting properties of concrete after replacing cement with fly ash are remarkably improved in artificial sewage.