Abstract: Online particulate matter detector is used in natural gas transmission stations to monitor particulate matter concentration in high pressure gas pipeline under different operational conditions, and to evaluate the performance of multitube cyclone separator. Results show that particulate matter concentrations are mostly below 0.1 mg/m³ under routine conditions, and may increase dramatically during pigging operations. Particulate matter concentration reaches a peak value of about 60 mg/m³ when the pig arrives, and then remains at a high level for a period of time after pigging. Generally, the pigging process can be divided into four stages in accordance with changes in particulate matter concentrations. By analyzing concentrations and particular size distribution at inlet and outlet of the multi-tube cyclone separator, its efficiency is determined to be 80% and above for the particles with diameter larger than 5 μm, and it can effectively remove the particulate matters with size above 10 μm. In summary, the separator plays an important role in protecting the downstream pipelines during pigging operations.