Hydrocracking is one of the commonly used oil processing technology, in which the process conditions are under high temperature and high pressure. For the oil contains sulfur and other impurities, the hydrocracking unit can be corroded easily. The ion chromatography and X-ray fluorescence spectrum are used to study the fouling problem occurred in 2 ^# hydrocracking unit E104 heat exchanger of SINOPEC Tianjin branch, and the causes of the corrosion fouling are analyzed from the scale of mechanism and nature of the material. The effective solving measures of fouling in hydrocracking unit heat exchanger are put forward.