Compared with the traditional steel and concrete pipe, the plastic pipe has big advantages， such as anti-corrosive, less leakage, light weight and easy installation. For normal buried sewage plastic structure wall pipe, its maximum ring stiffness is difficult to over sn 8. But in new pipe, stiffness can easily reach the surprisingly value of sn 8, sn 12. 5 and sn 16, even higher if necessary. In other hand, thanks to plastic properties, the plastic-steel-plastic composite structure could against corrosion very well.