Abstract: The small integrated nuclear reactor has drawn attention. On the basis of the NHR200-Ⅰ, the integrated nuclear heating reactor NHR200-Ⅱ was developed by Institute of Nuclear and New Energy Technology in Tsinghua University. The NHR200-Ⅱ reactor major loop thermal parameters were increased, and made it suitable for heating, industrial steam supply and sea water desalinization. In order to discover the natural circulation behavior under high temperature and pressure, the experiment study was needed. The scaling analysis provided the theoretical basis for determining the characteristics scale of the test facility. The similarity groups (Richardson number, etc.) could be determined using the dimensionless fluid and solid governing equations. In order to reduce the distortion, the test facility used the fluid with same property as the prototype. The axial length scale ratio and core surface average heat flux density ratio was 1∶1, and the flow area ratio was 1∶210.