In this work, the Fe-based amorphous powder/S-glass fiber reinforced epoxy composite panels of different amorphous powder and gradient layer structure were prepared by mould pressing method. The waveguide method and arch form method can be used to measure the electromagnetic parameters and the reflectivity of the samples respectively in the frequency range from 2GHz to 18GHz. The results showed that the amorphous powders distributed evenly during the S-glass fiber reinforced epoxy layers and the main absorbing mechanism of composite panels is magnetic loss. The absorbing properties of samples improve with the increase of the Fe-based amorphous powder contents and the thickness of panels. The model of gradient layer structure has a significantly effect to improve the impedance matching between the samples and the air. Thus, the absorbing properties of the composite panels can be increased effectively. When the thickness of the gradient layer structure composite panels is designed at 4.8mm excepting the Al plate thickness with 0.6~1.3mm thickness of Fe-based amorphous powder/S-glass fiber reinforced epoxy, the absolute value of the reflection coefficient of the multi-composite panels is above 4dB in the frequency ranged from 2GHz to 8GHz and above 10dB during 8GHz ~18GHz.