Abstract: Aiming at the calculation of contaminated product volume of refined product pipeline, taking ^#0 diesel and ^#90 gasoline as two kind of batch transportation medium, the governing equations of contaminated product are established based on multiphase flow model. Calculation of the two cases, upward U-tube and downward U-tube, is made and the distribution cloud maps of mixed oil volume are obtained. The influence of different transportation sequence and hydraulic transient on the mass fraction of contaminated product volume is analyzed. Results show that the mixed volume of the trailing gasoline in the forward diesel is larger in the upward U-tube case, the mixed length is longer and the average mass fraction of each cross section is smaller than that of the forward diesel, the mixed volume of the trailing diesel in the forward gasoline is smaller, the mixed length is shorter and the average mass fraction of each cross section is smaller than that of the forward gasoline in the downward U-tube case. Therefore, the transportation sequence of forward gasoline and trailing diesel can reduce the mixed volume.