Abstract: Polythylene coating is a main kind of coating material for steel pipeline. Yet, it has disadvantages like being easy to crack due to environmental stress and low operating temperature.Comparatively, the two kinds of coating materials have their similarities: their flow indexes do not differ a great deal, their mechanical characteristics are the same. But polypropylene is higher in solidness and stiffness. The different characteristics is that polypropylene has a higher temperature resistance and is not easy to crack for environmental stress. But still, polypropylene has the disadvantage of being fragile under low temperature.Through modification, polypropylene has good impact strength, which will possibly be the first to replace polythylene for long distance oil pipelines, with active surface mediurm, which require low temperature for construction and high temperature for operation.