Fuel oil leakage of heat exchanger is a general question in the circulating water system of Chinas petrochemical industry. The hidden leakage in the heat exchanger of circulating water system makes it difficult to be discovered in time when it leaks. Thus it leads to a large amount of oil spill, the corrosion of water cooling equipment, and potential hazards of systems normal operation and safe production. Therefore, it is very important to develop one technology for safe production of the units and the long period operation of system that can promptly distinguish the leakage material and leakage spot. According to the vector angle method, programmings with VB6.0 that can auto analyze two liquid spectrograms and calculate the similarity. The results show that this method can evaluate the similarity of liquid chromatography very well and it can be used for the leakage detection of the refinery circulating water system.