Abstract: Si/SiC materials were treated respectively in vacuum and nitrogen atmosphere at 1 650,1 750 and 1 850 ℃.The transformation of microstructure in Si/SiC was investigated by means of optical microscopy,scanning electrion microscopy and X-ray diffraction.In nitrogen atmosphere the transformation mode was nucleation of α-SiC seed lamellae of base plane by interface energy drawn.In vacuum,two transformation modes of base plane nucleation and evaporation-coacervation were concurrently present,and β-SiC was transformed more quickly than in nitrogen atmosphere.The driven force of transformation increased with temperature.There was a little β-SiC phase present at 1 850 ℃ treated in nitrogen atmosphere,but single α-SiC phase porous material was obtained by treated at 1 750 ℃ in vacuum.