PM-200 Particulate Online Monitoring System is a new draw-out low concentration dust measuring instrument. The instrument adopts the draw-out dilution sampling to avoid high humidity water vapor influence on the measurement. It can use it for continuous online monitoring of particulate matter with high humidity and low concentration. Through the real-time measurement of light scattering modules and regularly by use of β-ray analysis unit calibration, the sampled fume ensures the long-term stability of the measuring results, especially suitable for measuring low concentrated dust after coal-fired power plant wet desulphurization and wet dedusting.