Abstract: Transmitting natural gas with oil pipeline both optimizes the city fuel structure and utilizes the surplus value of oil pipcline with super low throughput. However, there are many problems in this transformation. The systematical study on this transformation of pipeline is carried out. An assessment on the residual strength and life of oil pipeline is made. In the light of the problems of internal corrosion and hydrate possi bly produced after the transformation of pipeline, some effective approaches, methods and measures are presented.