Abstract: Scaling analysis lays a solid foundation for the design and construction of scale-down nuclear reactor thermal-hydraulic system test facilities. Developments were introduced and characteristics were discussed for different scaling methods. Assessment and scaling concepts were summarized for some of the exiting test facilities throughout the world. All these work would provide the reference for choosing scaling concepts in the reactor integral test facility. It can be seen that the linear method is limited because of the gravity accelerator ratio, and the power/volume method is simple and effective while it also has some weakness inherent due to the features of thin and tall. H2TS (Hierarchical Two-Tiered Scaling) method which is based on PIRT (Phenomena Identification Ranking Table) scales both the integral and the local phenomena. The similarity criteria of H2TS contain the fluid properties which provide the probability of developing different scaling concepts. The ACME (Advanced Core-cooling Mechanism Experiment) test facility which will be built in China is directed by H2TS method.