According to GB 5009.223—2014 "National Standard for Food Safety, Determination of Ethyl Carbamate in Foods", the ethyl carbamate in liquor was determined, and the uncertainty of the measuring result was evaluated according to JJF 1059.1—2012 "Measurement Uncertainty Evaluation and Expression". Analysis found that the uncertainty of the measurement results was independent of not only the internal standard concentration of the isotope or the volumetric volume of the standard solution series, but also the volume of the sample after processing. Moreover, the uncertainty component introduced by the internal standard solution only related to the volume of the internal standard liquid. The result of evaluation showed that the content of ethyl carbamate in liquor was 106 μg/kg, and the expanded uncertainty was 10 μg/kg. The main components and contributions included measurement repeatability of 60.8%, standard curve fitting of 18.0%, standard solution of 16.4%, and sample processing 4.7%. In these components of uncertainty, the standard solution and sample processing caused by the pipette capacity tolerance and repeatability uncertainty accounted for 19.4%, which was the main source of the two components. Other sources such as balances, glass gauges, temperature, etc. were negligible.