Abstract: CPP900-IW48 and CPP900-W2 N automatic welding equipment developed by China Petroleum Pipeline Research Institute was briefly introduced. Welding parameters in a long-distance pipeline project were briefly described. According to the requirements of national standards and project design documents, the mechanical properties of circumferential welds welded by CPP900 automatic welding system were analyzed by using Charpy impact test, tensile test, bending test and drop weight tear test. The experimental results showed that the circumferential weld with good mechanical properties could be obtained by adopting reasonable welding process in CPP900 automatic welding system. Result of engineering practice showed that CPP900 automatic welding system had a good performance in the welding construction of large diameter, large thickness and high steel grade long distance pipeline in China.