Abstract: In order to study the flow and heat transfer characteristics of narrow rectangular coolant channels in plate-fuel reactors, the research status and development trend of the heat transfer in mini-channels around the world were reviewed. Based on the related parameters and experiment requirements of NP engineering reactors, a set of experimental loops for thermal hydraulic two-phase flow was established to study and analyze the heat transfer characteristics in plate-fuel cooling channels. According to real reactor operational requirements, a test section consistent with the actual coolant channel was designed. The flow direction is vertically downward, and the double-sided heating method is adopted, and the flow passage gap size is 2.3 mm. The channel width is 67 mm (62 mm-heated width), and the runner length is 1000 mm (750 mm-heated length). It was verified experimentally. The results show that the apparatus is correct and feasible.