Abstract: The particle concentration and size distribution of dust in filter's inlet and outlet of natural gas pipeline are measured by means of high-pressure isokinetic sampling device and particle size analyzer. Site testing results show that the sampling device performs well in sealing and reliability, with good data repeatable capability, and is suitable for assessment of filter's separating effectiveness of high pressure pipeline. Average separating efficiency of filters is given using the results measured. The condensation of particulate inside natural gas pipeline is less than 1.0 mg/Nm³ in site measurement.