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 the influence of high humidity water vapor on the measurement. It can be used for continuous on-line monitoring of particulate matter with high humidity and low concentration. The sampled fume, through the real-time measurement of light scattering modules and regularly by use of β-ray analysis unit calibration, 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.