Abstract: Plugging meters are the most important online meters for measuring the concentration of impurities in sodium. In order to improve the accuracy of the plugging meters, a new calibration method, cold trap controlling method, was put forward. To determine impurity saturation temperature by cold trap in experiments, a closed-loop control model was used to control the temperature of the cold point, and the range of the temperature fluctuation of the cold point was ±0.5 ℃ in the experiment. 28 groups of experiments were conducted, and an empirical calibration curve of plugging temperature was obtained. After the calibration, the range of deviation is -0.654-0.653 μg/g, and the mean absolute deviation and mean relative standard deviation of experiments are 0.298 μg/g and 4.40%, respectively. The residual probability scatters into a straight line trend basically, and the residual obeys the normal distribution, so the calibration curve has higher credibility. The accuracy of the plugging meters is improved by cold trap controlling method, and this method is simple and easy to popularize.