Abstract: The perforations were found in tubing of a water injection well during tripping out the downhole string. The causes of tubing perforation were analyzed by macroscopic observation, chemical composition analysis, hardness test, metallographic examination, mechanical properties test, attachment analysis, scaling prediction and bacteria detection, energy spectrum analysis and corrosion simulation experiment. The results show that the tubing was affected by the downhole working environment and the composition of the injected water medium, and scale layers such as CaCO₃ and BaSO₄ were formed and attached to its inner wall, forming an under-deposit corrosion environment. Under the dual action of Cl^- and sulfate-reducing bacteria, the under-deposit corrosion in local sensitive areas was continuously intensified, which led to in corrosion perforation of the tubing.