For the study of variable diameter tube affects the quantity of sequential oil transportation of the refined oil, applying multiphase flow model, the 90# gasoline and 0# diesel oil as the object of alternate transportations, according to different variable diameter pipeline structure form and different tapered Angle on the oil transportation.The results show that the growth rate of the length of the mixing section decreases obviously and the length of the mixing section decreases for a short time when the mixing oil enters the sudden expansion pipe, then the length of the mixed oil section growth accelerated obviously, but inferior to the level before variable diameter and with the increase of taper Angle, the different length were mixed with different degrees of decreased; after the mixed oil section flows into reducing pipe, the length of the mixed oil section growth obviously larger, and appeared the trend of decrease, but still higher than before the variable diameter, and with the increase of tapered tube taper Angle, the length of the mixed oil section all have varying degrees of increase.