The effect of vapor water injection on the pollutant emissions is studied in laboratory natural gas burner CH4 / air, based on a confined axially symmetric geometry. The swirl diffusion flame is fully turbulent. It is first verified that the laboratory burner reproduces the trends measured on industrial systems, in terms of pollutant global emissions when water concentration is increased. The detailed study of the laboratory burner includes local measurements on profiles at different height in the flame of temperature (thin thermocouple), velocities (LDA) and chemical species (CO2, CO, NO, O2) concentrations (analysis system). Flame maps obtained by planar Laser Induced fluorescence of OH are performed. Results obtained for three different values of specific humidity namely 0, 58, and 78 gram H2O per kg of dry air, are presented, and compared with results obtained by numerical simulation of the burner, using the computational fluid dynamics code Fluent.