In order to analyze the influence of gas liquid ratio on the combustion of liquid centered swirl coaxial injector, hot tests were conducted with a combustion gas generator under different gas liquid ratio. This combustion gas generator was equipped with liquid centered swirl coaxial injector. The results show that there exist three combustion conditions: stable combustion, transition from stable combustion to low frequency combustion instability and low frequency combustion instability. The low frequency combustion instability is not related to the oscillation of the supply system. It occurs because the triple flame moves away from the injection panel, when the triple flame arrives at the point of the impinging sprays, the stability of the triple flames decrease rapidly, making the flame front oscillating in the recirculation zone.