Abstract: The large-scale separating type heat pipe has been proposed to replace the active cooling system for passively removing residual heat from nuclear power plant, and experiment studies on such system become imperative. The experiment study on heat pipe made of the stainless steel 304 was carried out using R134a as the working fluid. The thermal performance (the heat transfer rate) and the temperature distribution inside the evaporator section were obtained. Furthermore, the effects of the hot water temperature at the inlet and the air velocity outside the condenser section on the operation temperature, heat transfer rate, heat transfer coefficient and flow rate of R134a were analyzed. The results show that the sub-cooled R134a entering the evaporator section evaporates and finally is overheated. The two-phase region as long as 6.6 m dominates the evaporator to ascertain the good heat transfer performance of the heat pipe. The maximum heat transfer rate is as high as 21 kW. Parametric analysis shows that the heat transfer is improved by the increase of hot water inlet temperature and the air velocity. The effect of hot water inlet temperature is more significant compared with the air velocity. The effect of the air velocity is obvious when it is small. As the air velocity increases, the increase of the heat transfer rate declines. To quickly predict the heat pipe performance for the design in the engineering, the correlation between the heat transfer rate and the average hot water and air temperature difference is developed.