The automatic Kjeldahl nitrogen analyzer method was used to detect the protein content in yuba,and the uncertainty of the detection process was analyzed and evaluated to further improve the quality control of the detection process.The results show that when the protein content in yuba is 43.2 g/100 g,the expanded uncertainty is 1.6 g/100 g(at 95%confidence interval,k=2).The uncertainty introduced by the instrument and the uncertainty introduced by the repeatability of the detection process have a significant impact on the detection uncertainty.