Abstract: In the past time, the optimal design for products pipeline focused on finding the optimal points of station parameters such as pipe diameter, thickness, numbers of pump stations, suction/discharge pressure, etc.. It seldom took the impact factors of oil blending into consideration. The paper briefly introduces the impact factors for oil blending in batch products pipelines as follows: the non-uniform distribution of the vertical fluid velocity; the turbulent diffusion of the fluid flow in both vertical direction and axial direction; the resorted oil in dead section; the elevation difference; the density difference for varied batches; the potential shutdown of the pipeline, etc.. With reference to the advanced experiences from international pipeline operating companies and taking cutting down the contaminated volume as a subject, the optimal design program are discussed in the allocation of relief tank and valves, the design of pig launcher/receiver's diameter and their manifold, the starting-up way for pump units, the diameter design for station pipeline and Re number for transported medium.