Abstract: The concepts of X-ray stress measurement error and uncertainty were clearly distinguished, and the sources and solutions of errors were explained. The methods for selecting and determining test uncertainty in the standard GB/T 7704—2017 were discussed, and the sources of uncertainty were analyzed. The results show that the sources of uncertainty in X-ray stress measurement were caused by the tested material and random effects. The selection of material microstructure, equipment status, and measurement conditions all affect the uncertainty.