The compositionally modulated amorphous films FeSi/Si have been prepared successfully. Systematically varying the thickness dm of the FeSi layers with fixed thickness of Si layers, it is shown that the saturation magnetization Ms decreases monotonously with decreasing dm. This basically is the contribution from the dead layer effect. The thickness of dead layer at OK is about 5.8?. With decreasing dm, the modulated films transit from three dimensional magnetism to two dimensional one gradually. The expressions of this transition are the appearances of low magnetic and nonmagnetic hysteresis effect, the linear Ms(T)-T relations and the monotonous decreasing of Curie temperature Tc. Tc satisfies the equation: △Tc∝dm-1, where λ=1.6.