Abstract:This paper mainly analyzes the source of uncertainty of standard meter method liquid flow standard device according to JJG643-2003 Flow Standard Facilities by Master Meter Method. MATLAB software was used to obtain the flow-meter coefficient curve by using the least square method, and the class A measurement standard uncertainty u1 of the standard flowmeter was determined; Based on the "black box theory", ignoring the complex digital-to-analog conversion relationship in process control, only focus on the "input-output" relationship, use the standard multi-function calibration source 5500A to calibrate the standard device, and obtain the uncertainty u6 of data collection, signal processing, data processing and communication; Finally, the extended uncertainty of the device U=0.27% (k=2); It provides a reference for the uncertainty assessment of related standard devices in the future, it also has certain reference significance.