Abstract: The effects of introduction methods of SiC on TEM structure and mechanical properties of 20wt% nano SiC/MoSi₂ composites prepared by reactive melt infiltration were studied. The results show that, the nanometer scale of matrix phase and reinforced phase of SiC/MoSi₂ composites can be obtained in the process of complete in-situ reactive infiltration silicon, but maybe due to the large number of fault defects inner crystals of the structure, the mechanical properties of the nano SiC/MoSi₂ composites improve not too much; when preparing the composites in partial in-situ reactive melt infiltration method to relieve the severe phase reaction, the defects inner crystal in nano SiC/MoSi₂ composites disappear, and there are a large number of tear ridges in the fracture, also, the mechanical properties of composites increase obviously due to the introduction of SiC initial powder.