Abstract: The application of downhole oil water separation technology is restricted by the complicated design system and rigorous requirements for candidate wells.The design method of downhole oil water separation system is investigated in this paper.The structure and principle of the system is introduced firstly,and the flow behavior in the subsystem and the coupling between them are studied before a system designing model is developed using the node analysis method.An example is also presented in this paper.The sensitivity of parameters are analyzed,and results show that the hydrocyclone,acting as an energy divider,is the core of downhole oil water separation system,and the production of oil formation as well as the injectivity of injection zone have great impact on the designing result.The model provides reliable basis for the field application of the downhole oil water separation technology,and it is significant to the application of the technology.