The correlation between initial permeability μi and temperature T(μi-T curve) for the Fe73.5Cu1Nb3Si13.5B9 alloy annealed at 300—610℃ was investigated.Three types of μi-T curve were observed. The corresponding annealing temperatures are (1)Ta≤460℃,(2) 480℃≤Ta≤580℃,(3) 590℃≤Ta≤610℃.The phase structures of the alloy corresponding to the three types of μi-T curve were analysed and the mechanisms for the changes of μi with T were also discussed.