Many gas turbine operators have reported low-frequency pressure fluctuation during the change of combustion load and near flammability limits. It is expected that the low-frequency pressure fluctuation is connected to flame destabilization due to changes of local equivalence ratio or flow conditions and that this fluctuation occurs readily near the lean limit and during load change process. Regarding the low-frequency pressure fluctuation, it is noticeable that many real gas turbine combustors operate under unchoked fuel flow condition, which can be affected by the pressure fluctuations of combustion chambers. In unchoked condition, interaction between fuel flow and pressure fluctuation can result in modulation of the fuel flow. This in turn brings changes to the spatial and temporal equivalence ratios, as both spatial and temporal heat production are highly related to pressure fluctuation.