Automatic dewatering system is an important device for dewater of crude oil storage tank. The appropriate selection of automatic dewatering system has direct influence on the basic sediment and water specifications of crude oil. This paper analyzed the water removal principle and structure of the automatic dewatering system. On this basis, this paper studied the selection of automatic dewatering system for crude oil storage tank. The study results show that: 1)The automatic dewatering method should be selected for crude oil storage tank dewatering;2)For heavy oil products with high variations in density and viscosity, it is recommended to use a liquid column resonance type pipeline automatic dewatering system, as this type of automatic drainer can handle both stable and unstable oil-water interface, and it is simple to install and easy to maintain;3)For clean light oil with clear oil-water interface, it is recommended to use an automatic dewatering system with a mechanical float, as it is not easily affected by the emulsified layer and it can easily detect the water content in the oil. The research results could provide guidance for the selection of automatic dewatering system for crude oil storage tank.