A　numerical　study　on　methane/air　combustion　inside　a　microchannel　was　undertaken　to　investigate　the　effects　of　geometry　of　microchannel　on　combustion　characteristics.　The　simulation　results　show　that　the　flame　front　shifts　downstream　and　the　distribution　of　temperature　gradient　and　reaction　rate　decreases　as　the　gap　increases.　When　the　gap　of　microchannel　equals　to　0.6　mm,　the　temperature　of　walls　and　fluid　temperature　in　areas　after　flame　both　decrease　with　the　walls　thickness　increase　from　0.1　mm　to　0.2　mm.　Whereas,　when　the　walls　thickness　is　larger　than　0.3　mm,　it　has　a　little　effect　on　fluid　and　walls　temperature　as　the　walls　thickness　increases.　When　the　gap　of　microchannel　equals　to　1.0　mm,　the　walls　temperature　and　fluid　temperature　decrease　with　the　increasing　of　walls　thickness.