Abstract: According to the operation condition of nuclear heating reactor, the thermal hydraulic experimental system for steam generator instability was set up, and experiments on steam generator instability under low pressure were carried out in this system, including the effect of flow resistance at the steam generator inlet, operation load and the steam pressure at steam generator outlet on the instability of the steam generator. The experimental results show that the thermal resistance ratio at inlet of the system, operation load and the system pressure have affection on the stability of once through steam generator, and the oncethrough steam generator can be stably operated under low parameter condition by setting up suitable thermal resistance ratio at inlet of the system.