Abstract: There were cracks in the short tube used for installing the liquid level meter on the outer wall of the secondary inlet separator cylinder of a natural gas unit. The cracks were located in the pipe base material area, which were circumferential cracks. Macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscope analysis and stress analysis were used to comprehensively analyze the causes of short tube cracking. The results show that there was still liquid accumulation with corrosive medium at the root of the first to second threads in the pipe fitting zone. This region initiated cracks under the long-term action of alternating load and the coupling effect of tensile stress and sulfur ions; the insufficient matching size of the level gauge and the short tube, the small stress area of the pipe wall, the increase of stress and the corrosive medium promoted the further expansion of the crack.