Abstract: In the light of the corrosion and leakage of A3 steel tank of ethylene dichloride, a defect detection and microscopic inspection have been conducted. It is found that the corrosion layer is laminated with stalactite. The corrosion mechanism of ethylene dichloride is analyzed. It is pointed out that the major cause of corrosion of A3 steel tank originates improper storage of ethylene dichloride, the HC1 produced from ethylene dichloride adsorbs water to form hydrochloric acid to result in electrochemical corrosion. Based on the analysis results, the safe storage method of ethylene dichloride has been made.