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.

Because of the natural life of the pipeline and the impact of artificial factors, pipeline leakage accidents occur frequently. It is very important to detect pipeline leaks and determine the leak location to minimize damage and maintain the safe operation of the pipeline. Be aimed at the products pipeline leak, the CFD simulation software was used to simulate changes in the pipeline pressure. Once the pressure changed at the pipe end and beginning, the pipeline leak happened somewhere. Then under the pressure gradient changes of the pipeline end and beginning, the pressure gradient method was used to ultimately determine the leak location of the pipeline. 