Abstract: Annular fuel has a special configuration of dual cooling channel. In this paper, based on computational fluid dynamics （CFD） method, a detailed fluid-solid-thermal coupling numerical calculation model for single annular fuel rod was established. The value range of flow distribution ratio (φ) of annular fuel was studied by calculating the temperature distribution of internal/external cladding and internal/external channel cooling water. The results show that the internal/external cladding temperature difference and the internal/external channel outlet temperature difference decrease with the increase of φ. The slope of the radial temperature curve inside the cladding appears abrupt change near cladding surface when φ≤0.72. And the temperature change inside the cladding is uniform with no sharp temperature change phenomenon when 0.86≤φ≤1. Moreover, the internal/external cladding temperature difference is less than 8 ℃, and the internal/external channel outlet temperature difference is less than 10 ℃. Considering the advantages of bilateral cooling capacity and the mechanical safety of the cladding, the value range of φ is determined to be 0.86-1.