The work aims to study the failure behavior of pipeline in black water treatment system of coal gasification, so as to clarify the failure features, analyze the failure mechanism and influencing factors, provide measures for avoiding the failure and extend the service life. Scanning electron microscopy (SEM) was used to detect the morphology of the pipeline. Corrosion products were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The flow field was simulated and analyzed through computational fluid dynamics (CFD). There were obvious water was hout morphologies in the inner wall surface of the failed pipeline, which was covered with small pits and brown loose porous corrosion products. EDS results showed that the suface elements were mainly Fe, S and O. The main corrosion products were FeS, Fe3O4 and FeO after further detected by XRD. CFD simulation was consistent with the actual ones well. The changes of secondary flow, particle size, velocity and Stokes number had a great influence on the trajectory of solid particles, and further affected the location of high-risk areas of pipeline erosion. The main reason for the failure of the pipeline is the coupling of H2S in the black water corrosion and pulverized coal particle erosion. The outer arch exit position in the elbow area and the bottom horizontal tube bottom position are the main high-risk areas. The high-risk areas of pipeline are effected by many factors and should be prevented in advance accordingly. Besides, the proper reduction of fluid velocity in actual work can reduce the erosion and protect the pipeline.