Abstract: Early leakage occurred in a stainless steel plate heat exchanger. The leakage causes of the plate heat exchanger were analyzed by means of chemical composition analysis, macro and micro observation, energy spectrum analysis, metallographic examination, non-metallic inclusion analysis, hardness test and water quality analysis. The results show that the water quality of circulating water was abnormal, and the high chloride in it caused pitting corrosion of the stainless steel plate of the plate heat exchanger. With the increase of pitting corrosion degree, the perforation leakage of plate heat exchanger was caused.