Advanced gas turbine adopts axially staged combustion to achieve the goal of increasing turbine inlet temperature while limiting NOx emissions. The premixing effect of secondary fuel injection has a significant influence on secondary combustion organization and flame-dynamic characteristics. In this paper, we proposed a novel twin-nozzle configuration for secondary fuel injection. Secondary fuel is injected from the front nozzle, and air is injected from the rear nozzle. Operation condition studied includes the diameter (d) of front and rear nozzle from 1 mm to 3 mm, jet Reynolds number from 1900 to 5700, the jet spacing L ranges from 2d to 4d, and the equivalence ratio of primary stage from 0.72 to 0.59. This flexible configuration controls the injection of fuel and air separately and allows fully lifted flame front organization, which is crucial for fuel/air mixing and NOx control. Using high-speed CH* imaging, the effects of primary stage equivalence ratio, nozzle diameter, and rear air injection ratio on the dynamical characteristics are investigated. We discussed the flame propagation mechanism, flame base pulsation frequency, ignition delay distance, and heat release distribution. We found that when the jet Reynolds number is reduced from 5700 to 1900, the flame pulsation frequency rises from 176 Hz to 586 Hz. When the rear air injection ratio increases from 0 to 3, the pulsation frequency decreases from 586 Hz to 88 Hz, the flame lift-off height increases, and the ignition delay distance decreases.