Abstract: In NaK alloy heat transfer system, the capability of heat transfer and mechanical properties could be seriously impaired by impurities, which requires methods to control the concentration. The cold trap plays the key role in purifying NaK alloy in the system and controlling the impurity under acceptable level. In this paper, a precipitation type cold trap working with forced circulation was chosen, and the flow and heat transfer performance was studied. The characteristic curve was obtained, by using the CFX program to simulate different work conditions and comparing with the experimental data. The optimization suggestion was also given.