Being aimed at the problem of contaminated oil in batch transportation of the same gasoline and diesel on different density condition during product oil flowing through the downhill and uphill, with the help of VOF model, the numerical calculation of threedimensional flow model was established. The influence of contaminated oil from different sequence，density，pipe range on boundary layer region was researched on the uphill and downhill road. The results showed that for uphill pipeline the length of the mixed oil of forward diesel was longer than forward gasoline，and the mixed oil volume of forward diesel was greater than forward gasoline. For downhill pipeline the length of the mixed oil of forward gasoline was longer than forward diesel and the mixed oil volume was greater than forward diesel. During forward the same gasoline and trailing diesel for different density diesel, the smaller density could help reduce mixed oil volume.

In batch transportation of finished oil products, mixed oil would be produced by adjacent batch oil. The cases of 30°, 45°,60° or 90° for the joint line of the variable diameter part and the straight pipe of the variable diameter pipe were calculated by the CFD software. The conclusion show the relationship and the change law between the angle of the joint of the variable diameter part and the length were researched. The results show that with the angle increased, the mixed oil segment length decreased in the sudden expansion pipe and the opposite conclusion in the reducer, which was coincided with engineering basic phenomenon.