Abstract: Plugging meter can realize the quantitative measurement and real-time monitoring of non-metallic impurity content before filling liquid metal working medium and during system operation. At present, related research work of sodium plugging meter has been carried out in China, to meet the impurity measurement requirement of the NaK alloy system, the flow characteristics and impurity precipitation process in the plugging holes are analyzed in this paper, and the theoretical basis for the design of plugging holes is summarized. Furthermore,the response lag coefficient is introduced. The plugging meter is tested on the ATC-R electromagnetic pump circuit after manufacturing. Accuracy of the plugging temperature is proofed by comparing with the cold trap operate temperature. The results also show that the plugging temperature has good stability and the random error is no more than 1%. Finally, the flow rate through plugging holes is suggested to be above 0.7 m/s, while the cooling rate should be within 1.5～2.5 ℃/min by experimental research and analysis.