Abstract: The condenser of a 135 MW thermal power generation unit leaked from time to time. In order to find out the leakage cause, the macro and micro morphology of the stainless steel pipes in the condenser was inspected during the shutdown and maintenance. There are several leakage points in the stainless steel pipes at the steam turbine side, and the leakage points mainly present the following two features: being scratched and being dented and perforated. In addition, the material of the condenser pipes and the quality of the circulating water were tested, and micro morphology observation and energy spectrum analysis the scale deposit in the pipes were carried out. The results show that the main reason for the condenser leakage is that the deposition of microbial slime accelerated pitting corrosion and led to corrosion under scale deposit, and the effective rotation of the ties caused mechanical wear on the inner wall of the pipes to a certain extent.