FeCo hollow fibers can possess high anisotropy field due to their high aspect ratio. Thus composite sheets containing these fibers are applicable to nearfield electromagnetic wave absorption sheets in 1~10 GHz region. For an understanding of the high frequency properties of the composite sheets, the Landau-Lifshitz-Gilbert (LLG) equation including eddy current effect and the effective medium theory with an additional magnetostatic correction were applied to simulate the frequency dependency of their magnetic properties.