Abstract: 6.5wt% Si silicon steel was prepared by chemical vapor deposition (CVD) method and the effects of reaction temperature，oxygen content in atmosphere and SiCl4 content on the brittleness of 6.5wt%Si silicon steel were studied using SEM, EDS and self-developed three-point bending machine. The results show that the grain size of the silicon steel increased with the reaction temperature rising, and the brittleness of the silicon steel increased with the increase of the grain size. Grain boundary oxidation was observed in the silicon steel when oxygen content in atmosphere was 100 mg·kg-1, which increased the brittleness of the silicon steel. Kirkendall voids were found in the silicon steel with a relatively high SiCl4 content of 35vol%, which increased the brittleness of the steel.