In the sewer pipes, reinforced concrete pipes and concrete pipes are mostly used. However, it is difficult to ensure the long-term durability of the pipe due to the corrosion of the rebar which is used for the reinforcement of the concrete. Also, reinforced concrete pipes are difficult to secure watertightness due to deterioration and corrosion by hydrogen sulfide. In order to solve such problems, research on using sewer pipes made of plastic materials is being actively conducted. When soil pressure and live load act on the buried flexible pipe, the load acting on the pipe is transferred to the surrounding soil. So, the flexible pipe will support the load with the surrounding soil together. It is difficult to predict these behaviors theoretically and clearly. Therefore, the design equation for the buried flexible pipe is analyzed by adopting theoretically idealized assumptions and it is estimated through experimental studies that it is similar to the actual structural behavior. In this paper, the mechanical properties of the soil and the polyethylene pipe were considered in application of the method proposed in ASTM D 2412 to design the buried polyethylene pipe. Also, structural behavior of the pipe resisting external loads such as soil pressure was investigated to use a polyethylene pipe as the buried pipe and the long-term behavior of the polyethylene pipe was predicted by the compaction rate of surrounding backfill soil through the field test.