In this study, flame dynamics of secondary fuel injection control is investigated by large eddy simulation (LES) in a lean premixed combustor to elucidate the experimental two-stage oscillation suppression phenomenon. Without secondary fuel injection, large-amplitude longitudinal oscillations were observed in the experiment. With constant injection of secondary fuel, the oscillation amplitude was reduced and with harmonic feedback injection, it was further reduced. In this process, the flame shape and the dynamic behavior of the flame were changed. To fill the gap of the experimental data and to understand the flame dynamics, large eddy simulations are carried out. The LES results show that the oscillation reduction is attributable to the roles of both the main flame and the secondary flame. The interaction of the main flame and the vortices is reduced when the injection is on; namely, heat fluctuation is reduced. The secondary flame helps the flame base stabilization and directly modulates the heat release in the feedback injection. The phase relations between the pressure, secondary heat release, and injection velocity are also shown. With these effects from the main and secondary flames combined, the oscillations are suppressed by secondary fuel injection. The present study indicates that LES can be a tool to understand flame dynamics with control. (c) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.