Abstract: The mechanism research of water ingress accident in high-temperature gas-cooled reactor (HTR) has a significant meaning for the safety of HTR. The flow and heat transfer of droplet in the steam generator annular channel were simulated by using single droplet model and solved by Runge-Kutta method in this paper. The results show that the droplet cannot reach at the top of the annular channel if the droplet’s initial diameter is less than 420 μm. The change of helium pressure has little effect on the droplet’s evaporation time and maximum movement distance.