In Na 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 Na in the system and controlling the impurity under acceptable level. In this paper, a precipitation type cold trap working with forced circulation was chosen, the size of inlet and outlet pipe, regenerator, return tube and also the size of air cooled related component were determined. The characteristic curve of cold trap was obtained by analysis of different work conditions, such as inlet mass flow, inlet Na temperature, air inlet temperature and mass flow of air. The flow and heat transfer performance of cold trap was studied. The optimization suggestion was also given.