The sensors used for measuring the oil concentration of the sewage discharged from ships are studied. The research is conducted based on Lambert Beer's law,and the basic principles of Rayleigh scattering and scattering-transmission ratio method, and optical turbidity method. By using the right angle dual channel structure design,to determine the intensity of the scattered light and transmitted light in mixture of oil and water;and by adopting the scattering - transmission ratio method to calibrate the content of mixture. The design includes hardware circuitry of the oil concentration sensor,software,and experimental and detection test devices. The experimental results show that the sensor using scattering - transmission ratio method can well meet the regulations about oil content metering specified in guide specifications related to ships oil discharge monitoring and control systems.