Nanocrystalline FeB alloys have been prepared with optimized grain size and inteal stress. Samples prepared under different annealing conditions are analysed by x-ray diffraction, and the permeability μ(ω) is measured by HP8510B Vector Network Analyser in the frequency range 2-18GHz. The results show that annealing leads to the growth of the grain size and reduces the inteal stress, and smaller grain size and larger inteal stress favours the magnetic dissipation.