Abstract: Experimental research on the heat transfer characteristic of liquid sodium flowing in annulus was done. On the basis of the experimental data, the flow regime was divided into laminar flow (Re≤2 000), transition flow (2 000<Re≤4 000) and turbulent flow (Re>4 000). Correlations for the friction coefficient and heat transfer characteristics in different regions were obtained respectively. The results show that the flow characteristics of sodium are similar to those of water. In the laminar flow, the friction coefficient of liquid sodium is a little higher than that of water, while in the turbulent flow, they are almost equal. The heat conduction takes up a large part in the heat transfer process, and Nu increases with Pe.