Amorphous Fe78 Si9 B13alloys have been treated by pulsed magnetic field with lowe r frequency. The macrostructural change of amorphous specimens after treatment were observed by mssbauer spectroscopy and TEM etc.This investigation show that nanocrystallization of amorpous Fe78 Si9 B13occurs under the con ditions: pulsed fiel d 16—32kA/m,pulse frequency 20—25 Hz,acting time ≤2min. The grain size of nano crystalline phase Fe(Si) is about 10nm. And, the temperature rise of specimens during the course of the application of pulsed magnetic field is very low(ΔΤ≤20℃).