For the purpose of studying the diffusion behavior of hcp Mg–Al–Sn alloys, several Mg–Al, Mg–Sn and Mg–Al–Sn alloys were prepared and assembled into ten diffusion couples annealed at 723, 773, 823 K separately. With the aid of the electron probe microanalyzer technique and efficient CALTPP (CALculation of ThermoPhysical Properties) software, the composition dependent interdiffusivities at various temperatures were calculated. After that, the atomic mobilities were evaluated according to the obtained diffusivities in conjunction with available thermodynamic descriptions of the system in literature. Extensive comparisons between the model-predicted and experimental data on diffusion behaviors indicate the reliability of the presently obtained kinetic parameters. It worth noting that the measured composition profiles and diffusion paths can be logically predicted merely with two ternary interaction parameters. The currently obtained atomic mobilities will serve the high-throughput computation design for multi-component Mg alloys.