Abstract: Based on the similarity criteria derived in theoretical model in scaling analysis for one-dimensional natural circulation, the methodology to determine the characteristics parameters of an integral facility was discussed. The results show that it is more reasonable to simulate the natural circulation phenomena using an integral facility of small-scaled, same pressure, and same working fluid. Both the similarity criteria of single-phase and two-phase natural circulation can be preserved and there is no obvious scaling distortion due to the transition of the scaling ratios. However, the cost of this kind of facility will be high. If using low-pressure facility to simulate high-pressure phenomena, the cost will be lower, and the test can be carried out more easily. But the transition of some scaling ratios from single-phase to two-phase natural circulation will not be smooth. For example, if keeping the same power ratio, the velocity ratio and the time ratio will be different.