The structure of Fe73.5Cu1Nb3Si13.5B9 nanocrystalline material as a function ofannealing temperature was investigated by X-ray diffraction（XRD） and positronannihilation technique（PAT）. The experimental results indicate that the amorphoussample startS nucleation and primary incrystallization at 480℃

and b.c.c. α-Fe（Si）solution separates out from the matrix. The amorphous diffusion peak decreases andthe crystalline diffraction peaks increase with annealing temperature. The crystallinefraction and the average distance among atoms in amorphous phase as a function ofannealing temperature are computed based on the diffraction spectra. The PATexperiments prove that the amorphous Phase at grain boundary mainly containing Nband B atoms exists in the sample after annealing at about 550℃。The change ofS-parameter is in accordance with that of the atomic average distance in amorphousphase with annealing temperature.