Abstract: A coal gas pipeline broke in use process,some analysis methods were used including chemical analysis,macroscopic fracture,mechanical property and microstructure analysis. The results showed that there were some shatter cracks on the inside and outside surface of pipeline,some pores existed in the material,and the microstructure was nonuniform,that led to the mechanical property was not meet the requirements,under the outside force the pipeline broke. The improvement measure was put forward at last.