The unsteady supersonic flow over tandem cavities has been analyzed by the integration of Navier-Stokes equations with the κ-ε turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. The upwind TVD scheme based on the flux vector split with the van Leer limiters is used. The results show the principal frequency is very been analyzed by the combination of the several aspect ratios of cavities are almost same, because two shear layers aspect ratio, the frequencies of tandem cavities are almost same, because two shear layers developed from each cavity of high aspect ratio, the characteristis of frequency are very different, because the second shear layer is developed in the diffused first shear layer.