The model combustor of aircraft engine under fuel-lean condition is characterized by planar laser-induced fluorescence (PLIF) technique. By imaging the fluorescence from OH and CH2O simultaneously under various operation points, the transient structures of the reaction zone and preheat zone have been investigated. By the application of proper orthogonal decomposition (POD) and extended POD (EPOD) methods to the OH PLIF and CH2O PLIF data, the main dynamics modes of the swirling flame are extracted, as well as the CH2O PLIF signal distribution for each POD mode. The experimental results indicate that as the thermal power of the combustor increases, the time-averaged structure and dynamics modes experience notable transitions. At relatively high flow rate, local extinction occurs and unburnt fuel emerges in the external recirculation zone (ERZ).