Abstract: In this paper, the optimal design process of a single heat pipe and its heat and mass transfer mathematical and physical model were established. Considering the working environment of the heat pipe, the heat pipe used for heat exchanger in the passive residual heat removal system of the nuclear reactor was completely designed, and its heat transfer characteristics were analyzed. The analysis shows that the composite wick heat pipe meets the heat transfer requirements of the residual heat removal system, and its heat transfer power is mainly affected by the capillary limit, boiling limit and total thermal resistance of the heat pipe. With the same wick thickness, the capillary limit of the composite wick heat pipe is 100% to 700% higher than that of the single wire mesh wick heat pipe. Changing the outer diameter of the heat pipe or thickness of the wick, that is, reducing the diameter of the steam cavity, the boiling limit significantly reduces. When the heat transfer power of a single heat pipe is greater than 1 kW, the length of each section of the heat pipe is 0.4, 0.2 and 0.4 m, the outer diameter is 30 mm, and the wick with a thickness of 2 mm is a composite wire structure of 400 mesh+50 mesh. This paper provides theoretical support for the design of high performance heat pipe heat exchangers and the analysis of heat transfer characteristics.