In　order　to　study　the　effect　of　spark　plasma　sintering　(SPS)　technique　synthesis　SiC-MgB2　on　the　phase　formation,　the　MgB2　and　SiC-MgB2　bulks　were　fabricated　with　mixed　powders　by　various　SPS　synthesis　routes.　The　phase　formation　processes　were　investigated　with　the　aid　of　X-ray　diffraction　analysis,　TEM　investigations　and　sintering　theories.　The　solid-solid　reaction　between　Mg　and　B　powders　formed　MgB2　at　low　temperature.　As　the　sintering　temperature　increases,　the　reactions　of　molten　Mg　with　B　form　MgB2,　and　simultaneously,　the　molten　Mg　promotes　the　decomposition　of　SiC　and　nuclei　of　Mg2Si　may　form　on　the　surface　of　SiC　grains;　the　nascent　MgB2　incorporates　the　carbon　into　lattice,　hereby　enhancing　the　SiC　decomposition.　The　experimental　results　are　in　good　agreement　with　the　assumed　chemical　reaction.