Freeze-thaw damage in cold areas often decreases the performance and service life of concrete structures. This work presents a mesoscopic numerical method to investigate the heat and moisture coupled transfer of concrete subjected to frost action at the meso-scale while accounting for phase change kinetics. In this method, a new multiphase hydrothermal coupled model is established to describe the coupling effects of heat exchange, moisture migration, ice formation, and vapor condensation in concrete exposed to freeze-thaw cycles. To consider its meso-structural characteristics, a meso-structure of concrete consisting of mortar, interfacial transition zones (ITZs) and aggregates is generated and employed to conduct some numerical simulations. Results indicate that the proposed mesoscopic method is capable of predicting hydrothermal behaviors of concrete at the meso-scale. The hysteresis of the evolution of relative humidity with temperature becomes more pronounced as aggregate content increases from 20% to 50%, owing to the role of phase change. In particular, the relative humidity of concrete containing 50% aggregates rises to 91% and then swiftly reduces to 85% as the temperature decreases. Furthermore, when the permeability ratio of the ITZ to mortar is reduced from 10 to 1, the ITZ diffusivity only affects the relative humidity during the thawing process.