Abstract: For medium and small city gas users (especially for civil gas). a remarkable flow fluctuation and gas with certain dust and impurity are common problems. To solve the problem, a TDS instrument suitable for field gas flowing envrioment and availability are selected from various metering insruments, A comparison test on the flowrate loss of TDS instrument is conducted at low flowrate so as 10 enhance metering capability of the instrument. The application of the metering instrument is recommended.