Abstract: For the initially commissioned gas transmission pipeline, foreign materials such as soil, water and light oil will enter into pipe, which is hazardous to the operation of pipeline and some facilities. To solve this problem, effective technical measures should be taken during pipeline's design, construction and operation. In the paper, the hazard of impurity and disposal method for gas pipeline are introduced. Suggestions to improve the design, construction and management of valve chamber and blowdown system are put forward.