Abstract: Plate-type fuel is extensively utilized in various of small testing-reactors and integrative-experimental-reactors for its high power density and deep burnup. Its long and narrow coolant channels are susceptible to bending deformation under common expected transients such as internal irradiation and flow-induced vibration, furtherly to influence the flow and heat transfer characteristics of reactor core, even to pose a threat to reactor safety caused by severe phenomenon like local sub-cooled boiling. Traditional sub-channel analysis code or lumped parameter method possesses rapid computational speed through model simplification, resulting in conservative calculation results while fine details of flow and heat transfer process are unable to be captured. Computational fluid dynamics (CFD) is an elaborate numerical simulation method developed in recent years which is capable of predicting three-dimensional thermal-hydraulic characteristics under various flowing condition in refined scale, but the high-resolution CFD simulation for entire reactor core requires enormous consumption of computing resource which can’t be satisfied by present technology. In consequence, a comprehensive model realizing both high computation speed and calculation accuracy for full-scale numerical simulation of reactor core possesses realistic significance. In this paper, a three-dimensional thermal-hydraulic characteristic analysis code CorTAF-PT developed based on opensource CFD platform OpenFOAM is widely used in energy and chemical industry, aerospace field, oceanographic ship field and many other areas. Taking inspiration from the sub-channel analysis method, the control volumes based on finite volume method were divided along the central plane of adjacent fuel plates. The coupled heat transfer model between fuel plates and narrow rectangular coolant channels was established through combining convective heat transfer between coolant and cladding as well as heat conduction in fuel plate. Under code validation against several flow and heat transfer experiments of narrow rectangular channels, multiscale three-dimensional numerical simulations of IAEA 10 MW material test reactor under bending deformation and steady-state were carried out by CorTAF-PT. Macroscopic and microcosmic distributions of pivotal parameters such as coolant temperature, fuel pellet temperature and cladding temperature of the entire reactor core were obtained. The maximum temperature values of coolant, fuel pellet and cladding are 326.71, 345.38 and 345.29 K, which are 2.65, 1.42 and 0.65 K changed than steady-state distribution respectively. And the deviation of hot spot was revealed and analyzed. This study has reference value for the development of high precision three-dimensional thermohydraulic analysis technology of autonomous controllable core level, and also lays foundation for the subsequent safety analysis of plate-type fuel reactor core under accidents.