The　effect　of　CO2,　which　replaces　part　of　N2　present　in　air,　on　flame　stability,　laminar　burning　velocities　(LBVs),　and　intermediate　radicals　(O　OH)　of　CH4/O2/N2/CO2　premixed　flames　has　been　analyzed　using　detailed　experiments　and　numerical　studies.　The　numerical　simulations　were　conducted　using　the　PREMIX　code　with　a　detailed　chemical　reaction　mechanism　(GRI-Mech　3.0)　and　a　reduced　mechanism　(39　species　and　205　reactions)　based　on　GRI-Mech　3.0　over　a　wide　range　of　equivalence　ratios　(Φ　=　0.7-1.3)　and　CO2　substitution　ratios　(0-30%).　The　reduced　mechanism　showed　a　good　agreement　with　the　other　detailed　mechanisms　and　experimental　data.　The　experimental　and　numerical　results　showed　that　the　substitution　of　CO2　diminishes　the　stability　of　the　flame,　and　the　flame　blow-out　speed　is　significantly　reduced　(the　substitution　ratio　is　0-30%,　and　the　corresponding　flame　blow-out　velocity　is　5.2-2.5　m/s).　In　addition,　CO2　inhibits　the　LBV　of　the　flame　owing　to　the　decrease　of　O　and　OH　mole　fractions.　It　not　only　accelerates　the　consumption　of　these　two　free　radicals　but　also　inhibits　the　generation　of　these　two　free　radicals.　Further　analysis　concluded　that　the　substituted　CO2　has　the　greatest　influence　on　the　LBV　sensitivity　coefficient　of　the　HO2　+　CH3　=　OH　+　CH3O　reaction.