Fe_Si_B_Nb_Cu alloy thin films were deposited by radio frequenc y (rf) magnetro_sputtering. Their microstructures have been analysed by x_ray di ffraction (XRD) and Mssbauer spectrum. The results show that the thin films, p repared by low rf power, are amorphous. With the increase of rf power, the depo sited thin films were turned to be a mixted structure composed of nano_crystals and amorphous matrix. The nano_crystals contain α_Fe(Si) and α_Fe(B) solid solutio ns, which are in nanometer size, their relative volume fractions, atomic assembly features , magnetic moment orientations and macro_magnetic properties are changed under d ifferent rf powers.