Abstract: An experimental study was conducted to investigate the characteristics of subcooled flow boiling heat transfer under low pressure and low flow velocity. By analyzing the thermal parameters and visual images acquired during the experiment, boiling hysteresis, boiling instability, and boiling heat transfer coefficient were explored. The experiment shows that the wall superheat at the boiling incipience is high, and the occurrence of boiling greatly increases the heat transfer coefficient, so there is a remarkable boiling hysteresis phenomenon. The relatively smooth heating surface can achieve a higher degree of superheat, while bubbles generated rapidly at low pressure is large in size, and the gas-liquid interface shows a significant disturbance at low heat flux, breaking the bubble into multiple small bubbles which serve as nucleation sites. In the prediction of subcooled boiling heat transfer coefficient, Dittus-Boelter convection heat transfer correlation is no longer applicable. The Hallman correlation and Gnielinski correlation were used to calculate the convection heat transfer coefficient, and the wall superheat was introduced to modify the pool heat transfer coefficient. The above procedure can greatly improve the prediction accuracy of the subcooled boiling heat transfer coefficient.