In this paper, the influence of annealing temperature on AC magnetic property of Fe15.38Co61.52Cu0.6Nb2.5Si11B9 nanocrystalline alloy is investigated, and the possible reasons for better high-frequency soft magnetic properties are analyzed. The resistivity decreases as annealing temperature increases. The value of μ'f0 is not in direct proportion to saturation magnetization Ms because of irregular variation of the gyromagnetic ratio with annealing temperature. At annealing temperature Ta=873 K, the alloy has the largest quality factor and relaxation frequency, i.e., Q(1 MHz)=23.1 and f0=25.02 MHz.