Abstract: In order to deepen the understanding of flash evaporation characteristics related to the coolant leakage under high-parameter conditions in the primary circuit of nuclear power plant, the thermodynamic characteristics of spray flash evaporation under high temperature and high pressure were studied based on the modeling method in this paper. The droplet motion, droplet heat and mass transfer and physical properties change were comprehensively considered in this model. The droplet temperature distribution, flashing efficiency and intensity of spray flash evaporation were calculated and analyzed. The results show that increasing the superheat can effectively reduce the distance needed for the finish of the flash evaporation and improve the flashing efficiency in a wide range. The decrease of the droplet size can lead to the obvious decline of the dimensionless temperature at the same position. The flow velocity mainly affects the spatial distribution of the droplet temperature and has little effect on the temporal distribution of the droplet temperature. The flashing efficiency decreases with the increase of the flow velocity within a certain area. Compared with the effect of the droplet size on the dimensionless temperature distribution, the effect of the droplet size on the flashing efficiency is relatively small. The effect of the droplet size and superheat on the intensity of spray flash evaporation has a turning point. The turning distance increases with the flow velocity.