The gas generator is the key equipment of scramjet ground test system. A kind of air/kerosene/water gas generator was designed in order to improve the system security and economy. A series of ignition performances experiments were conducted in the fuel-rich condition with the gas generator. The experimental results indicate that: the lower limit of excess oxidizer coefficient for reliable ignition was 0.51 with the gas generator. The injection of water, which lowered the flame propagation speed and reduced the chemical reaction rate, would make it difficult to ignite and stabilize the flame. The ignition reliability could be improved by increasing excess oxidizer coefficient. Simultaneously, the injection of water would easily cause combustion instability. Low frequency combustion instability can be damped by increasing excess oxidizer coefficient.