Study on the unsteady pressure distribution in case of oscillating and non-oscillating flat plate in uniform flow is discussed by Vortex Shedding Panel Method (VSPM), in which the unknowns of both vortex and source densities on the surface are signified, comparing with the observable facts. This paper also shows the comparison on the calculated results between VSPM and another calculation method (Finte-Analytical Method based on N-S equation) in order to evaluate the theoretical treatment on this kind of problem with the separation flow.