Abstract: The experimental investigation has been carried out at atomospheric testing rig to determine the effect of steam injection on combustion performance.The combustor used in the experiment was a modified WZ 5 annular combustor in which two steam injection sets were installed in the front and rear parts respectively.The tested fuel was gaseous fuel with medium heating value.The results show that steam injection had no impact on combustion efficiency and exit temperature pattern when the mass injection ratio (steam mass flow rate/air flow rate) is less than 5%.The exit temperature pattern factor increases and exceeds the acceptable value 0 25 to 0 30,as the steam mass injection ratio increases to about 10%.In addition,the test results also show that the process of the front part injection must be conducted smoothly,otherwise extinction of burning would occur.