Abstract: In the unloading process of light oil of tank car, the auxiliary unloading system of light oil pump controlling room is used to substitute the current vacuum unloading system. On the basis of theoretical analyses, simulation tests and application actuality, an optimized design on the structure of auxiliary unloading system is made. The site application of the newly-designed system shows that the new system has significant advantages than that of vacuum unloading system, which eliminates the defects existed in vacuum unloading system and can be widely used in petrochemical enterprises.