The “time marching” technique is successfully applied to the numerical computation of the nonstationary aerodynamics of a flat plate cascade for compressible flow of either subsonic or supersonic nature. The unsteady perturbation amplitudes of fluid properties are used as the dependent variables so that the computational domain can be reduced to a two-dimensional channel guided by two adjacent blades for any interblade phase angle. A new method of handling the boundary condition is developed in which the order of accuracy for the boundary points will be the same as the interior points. The wake region behind the trailing edge of each blade is treated as a “slip plane” as done in two-dimensional steady state supersonic flow. Results are in good agreement with existing analytical solutions.