Abstract: The swimming pool-type low-temperature heating reactor (SPLTHR) has low thermal parameters, large heat capacity, and high inherent safety, so it is a suitable reactor type for nuclear heating reactors. Because the SPLTHR has a long shutdown time and the temperature difference between the cold and heat sources is small, it has certain requirements on the heat transfer capability of the passive residual heat removal system (PRHRS). Basing on the characteristics of SPLTHR, a singlephase natural circulation experiment system of PRHRS of SPLTHR was designed by H2TS (hierarchical twotiered scaling) proportion analysis method, and the flow and heat transfer characteristics of the singlephase natural circulation of the PRHRS were studied experimentally. In order to get closer to the prototype system, the center height difference of the cold and heat source of the experimental system was the same as that of the prototype system, which was 9 m. The ranges of the pool water temperature, air temperature and air flow rate in the experiment were 50-90 ℃, 15-30 ℃ and 15 000-35 000 m3/h, respectively. The results show that the experimental system designed by H2TS proportion analysis method can achieve the designed heat transfer capacity when the temperature difference between the cold and heat source is 54 ℃, which means the method is suitable for the design of singlephase natural circulation system under low temperature difference. There is flow oscillation in the system startup process, and the system can be stabilized gradually with the operation. The hot and cold water in the primary loop alternately enters the heat exchanger and aircooler, causing the driving force of the system to change, which leads to fluctuations in circulation flow rate and heat transfer capacity. The change of boundary conditions mainly affects the heat transfer capacity of the system and the time to reach stability, but has little effect on the shape and number of fluctuations before the system reaches stability. For the PRHRS heat exchanger tube bundle, which is neither a constant heat flow nor a constant wall temperature boundary, it is more appropriate to use the natural convective heat transfer temperature difference as the parameter of the Grashof number. Due to the tube bundle effect, the traditional singletube natural convection heat transfer correlations have a low predictive value for the natural convection heat transfer outside the tube bundle. According to the experimental data, the correlation of natural convection heat transfer outside the tube bundle with the applicable range 3.51×103