The Fe32Ni32Si16B18Nb2, Fe31Ni31Si18B18Nb2 and Fe30Ni30Si20B18Nb2, (at. %) alloys are synthesized using low purity of raw materials by high power CO2 laser cladding with synchronous powder feeding. X-ray diffraction results show that the coating has an amorphous structure with some crystalline phases on it. The microstructure of the coatings changes with different amounts of Si. It can be observed that black nanocrystalline grains embedded in the amorphous phase in the TEM image. The coating of Fe31Ni31Si18B18Nb2 alloy was annealed at different temperature for 30 minutes and the microstructure were investigated. The highest Vickers Hardness had exceeded 1300 in the coatings. The amount of Si is a critical factor for fabricating a Fe-Ni based amorphous composite coating.