Abstract: Chemical composition analysis, macroscopic observation, metallographic observation, energy spectrum analysis and X-ray diffraction analysis were used to analyze the piercing failure reasons of ethylene cracking twisted-tape-tube. The results show that the piercing failure of twisted-tape-tube was caused by sulifide corosion. Some reasons, such as high oxygen and nitrogen content,cast defect (microshrinkage) and metallurgy defect (inclusions) with high sulfur content and sodium content, made sulfur detain and gather at defects positions and forme Ni-Ni3S2 low melting point eutectic, which accelerating local corrosion of internal wall of twisted-tape-tube and causing piercing failure at last.