In order to reduce downstream facility production loads or oil transportation loads, it is necessary to cut water in oil tank. There is a variety of water cutters selected for oil tank, but a large number of the cutters have poor water-cutting effect and only a very small number of water cutters can cut off water from pollutants and impurities. The main problems include inability to cut off water, not full water-cutting and oil leakage. Analysis results show these problems are related to improper water cutter type selection. When water cutter is selected, such issues shall be considered as actual project situations, practicability, reliability and economy of water cutter product. It is suggested that pipeline water cutter is selected for oil products with high density and viscosity, contaminants and impurities, especially toxic components and buffer tank type automatic water cutter is selected for clean light oil products with not high density and viscosity, which is more economical and reasonable.