Abstract: As the line pipe, the PP pipe just becomes popular in China. In the light of the fusion welding of PP pipe, an automatic fusion welding machine has been developed and is successfully put into operation in the construction of 12 km brine pipeline. The principle of fusion welding (thermoset opposite-extrusior method)and the development of automatic fusion welding machine as well as its performance are respec-tively introduced. Meanwhile, it is pointed out that the thermoset opposite-extrusion method is an ideal method for the construction of PP pipeline with a high availability.