Abstract: To increase the measuring accuracy of standard orifice flowmeter, the design, manufacture, test and installation on the throttle instruments of standard orifice flowmeter are carried out based on the domestic code of SY/T 6143-1996, and a kind of calculation software for the design of united standard orifice flowmeter and types selection of instrument. The authors consider that the following measures as applying the replaceable orifice instrument and set value throttling instrument, adopting reasonable flow rate totalizing method, eliminating the, factor of pulsating flowing, regularly retrogressing the metering value, carrying necessary training and establishing and improving metering regulations and system can effectively increase the metering accuracy of standard orifice flowmeter.