According to the optical activity of oil mist, the method of oil mist concentration detection based on optical rotation effect was presented. Basic principle of oil mist concentration detection system was introduced. The structure of detection system was designed. Mathematical model of detection system was established. Simulation and experiment research on the detection system was carried out. In oil mist chamber, linearly polarized light which is used as input optical signal is produced by polarizer and detected by analyzer. Using single-light-path detection method, detection system is compensated and modulated by Faraday modulator and calibrated by weighing method. Concentration information is obtained by photoelectric conversion. The experimental results show that the method has good linearity and stability, and detection effects are good when oil mist concentration is low.