Abstract: This article takes as an example a case where a company's evaporator, having been in operation for less than a year, experienced severe corrosion on the outlet side of the tube bundle. The corrosion causes were determined by macroscopic analysis, chemical composition test, hardness test, metallographic and scanning electron microscope analysis. The analysis showed that oxygen corrosion occurs in the evaporator tube bundle. After the unit is shut down, the residual condensate water in the tube bundle is not completely discharged, and accumulates at the outlet side, causing corrosion on the water side. The presence of Cl ions aggravates the corrosion.According to the causes of corrosion, some suggestions are put forward on the quality of the inlet steam and the maintenance of the equipment, which can provide reference for the subsequent operation of the evaporator.