Abstract: The principle, structure and experimental results of the manual plugging meterare described for measuring impurity concentration in sodium. In order to reducemeasurement error, we investigate some factors which affect accurate measurementof plugging temperature and have found the way to reduce the error. The experi-mental results show that the differences between the concentrations for the highplugging temperature and the low plugging temperature at different levels of im-purity concentrations are almost same. The difference for hydrogen is 0.0763 ppm,1.03 ppm for oxygen.