Abstract: The thermal-hydraulic risks of fuel assemblies during fuel transfer process should be considered according to the nuclear safety design regulations. Specifically, the natural circulation in complex flow paths, namely, the flow and heat transfer in narrow and horizontal region, should be investigated. Based on pre-research by computational fluid dynamics (CFD) method, the key section in the prototype was selected and main phenomena existed in this section were identified. Thereby the experiment facility was designed according to the requirements of experiment. Based on similarity theory, the deviation analysis between facility and prototype suggests that the errors led by deviation can be tolerated, and this facility lays a basis for further experimental research.