Abstract: The pressure gauge tube on absorption tower of a domestic chemical factory suddenly broke during operation, and the fracture position was near the tube weld. Through chemical composition analysis, macro-morphology and micromorphology analysis of fracture, metallographic structure analysis and fatigue life analysis based on S-N curve, the reason of tube fracture was explored. The obvious fatigue striation on the fracture surface indicates that the failure of the pressure gauge tube is fatigue fracture caused by vibration, and the vibration excitation of the main tube is one of the reasons for fatigue. In addition, the weld structure and welding form of the tube cause the position near the weld to be fatigue sensitive zone. Preventive measures are given in terms of improving the stability of the medium flow in the main tube, changing the structure size of the gauge tube, changing the structure of the weld seam. It is of great significance in preventing the recurrence of such accidents.