The influences of water vapor on the important chemical species in the methane reburning process were investigated on an electrical heated test rig with a nonintrusive multipoint sampling system. Experimental results with a stoichiometric ratio of 0.93 at 1100 degrees C temperature show that, in three different water vapor addition cases (7.8%, 3.9%, and 0.0%), water vapor reduces the consumption of CH4 and NO, and the production of CO, CO2, and HCN, but it enhances the production of H-2. The concentrations of O-2, C2H6, C2H4, C2H2, and NH3 typically are not influenced much by water vapor in the methane reburning process. The experimental result of water vapor for increasing the concentration of NO and decreasing of the concentration of HCN could be explained through the species reactions of H2O, H, OH, CH4, CH3, NO, and HCN via the reactions of OH + H-2 = H2O + H, CH4 + OH = CH3 + H2O, and CH3 + NO = HCN + H2O.