Abstract: As an important procedure of pipeline construction, the welding quality will directly influence the pipeline's service life and safety. Based on the analysis of site welding, the main welding defects are lack penetration, lack fusion, slag inclusion and porosity. According to some relative welding theories and bonding to the actual conditions of construction site, some analyzing work have been done on the four kind defects occured and influencing factors. Some eliminating methods are provided in order to eliminate the defects and enhance the welding quality. By means of these methods, some good results have been received. At the same time, some proposals for future pipeline construction have been put forward.