Flame characteristics and NO emission behavior in CH4/air-air premixed counterflow flames with applying FIR and FGR with CO2 and H2O were investigated numerically by varying the ratios of FIR and FGR as well as global strain rate. Chemical effects of added CO2 and H2O via FIR and FGR were analyzed through comparing flame characteristics and NO behaviors from real species(CO2 and H2O) with those from their artificial species(XCO2 and XH2O) which have the same thermochemical, radiative, and transport properties to those for the real species. The results showed that flame temperature and NO emission with FIR varied much more sensitively than that with FGR. Those varied little irrespective of adding CO2, H2O, and their artificial species to the fuel stream via FIR. However, Those were varied complicatedly by chemical effects of added CO2 and H2O via FGR. Detailed analyses for them were made and discussed.