Abstract: Propylene, the common petroleum gas, is subject to gasification under heating and liquification under pressure. Three simple ways are available to unload a propylene tanker; by pump, heating and pressurizing, or pressurizing by nitrogen. Unloading operation is seldom acomplished only by one of the three ways, because each has its operational limitations, such as heavy blowdown, unable to unload out at atmospheric temperature and unable to unload at high temperature, difficult to replenish the pressurizing tank, as well as nitrogen consumption, thus, the first way and second way or the first way combined with the third way are adopted, in which the former way has the advantages of fewer investment, wide operational range and perfect unloading process, and the way has proved itself to be high economical benefits to unloading operation for modified propylene tanker in Fushun Acrylic Fibre Factory.