Abstract: Based on a self-established mathematical model of oil evaporation loss (PEL) under unsteady conditions, a evaluation software of PEL is developed for the purpose of appraising the evaporation and discharge rule and calculating oil vaporizing mole fraction, evaporation volumes and losses in different kinds of oil storage and transportation equipment under different working conditions by computer easily and conveniently. The software can produce on-line tables and charts the vaporizing mole fraction distribution, etc., also can be used to evaluate the effect of the control methods such as the vapor recovery technology applied for cutting down the loss in oil products storage and transportation process, and/or for guiding the enterprise in energy saving management.