Abstract: The changes of microstructure, phase and composition of 3 % grain oriented silicon steel after solid powder siliconizing and diffusion annealing as well as their effects on magnetic properties were studied. The results showed that wellstructured compound layer could be prepared on grain oriented silicon steel by infiltrating silicon at 950 ℃ for 6 minutes，and the surface phases were Fe3Si and FeSi. After diffusion annealing at 1 050 ℃ for 1 hour，annealed samples with good organization properties were obtained. When the annealing time was 2 hours, a homogenized sample with the mass fraction of silicon close to 6.5 % (6.43 %) was obtained，and the surface phase was the single αFe phase. After solid powder siliconizing and diffusion annealing，the medium and high frequency iron loss of the sample was significantly reduced by 50 %~86 %，and the iron loss reduction rate of the sample annealed for 1 hour was higher. After solid powder siliconizing and diffusion annealing，the magnetic induction intensity decreased slightly.

Key words: grain oriented silicon steel, solid powder siliconizing, diffusion annealing, magnetic properties