Abstract: Permafrost is extremely adverse for a buried pipeline. It may seriously threaten the pipeline operation and damage the environment nearby. In this paper, with the finite element analysis and considering the seasonal variation of environmental temperature and the phase change of frozen soil, the depth at which the frozen soil can defrost is calculated when an intermittently-operating buried oil pipeline is not insulated, in order to demonstrate the necessity of pipeline insulation. Furthermore, for three insulation cases, i.e. phenolic, rigid polyurethane foam, and flexible polyurethane foam, the defrostation depths are calculated and their insulation effects are compared. On this basis, the design of insulation of pipeline buried in permafrost area is proposed.