Abstract: Due to its advantages of higher heat flux and wider operating temperature range, sodium heat pipes have shown promising application prospects in related miniaturized and unmanned nuclear reactor platforms. The accuracy of the working fluid’s evaporation accommodation coefficient (a_cc) in sodium heat pipes holds significant importance for their thermal transport analysis. According to existing research, it has been found that the evaporation characteristics of the working fluid are related to the contact surface condition, and the value of a_cc is significantly influenced by temperature. Therefore, the impact of different internal parameters and operating temperatures on a_cc of sodium within the sodium heat pipe was studied by using experimental methods. By varying parameters such as heating power, inclination angle, filling ratio, and capillary wick, the axial outer wall temperature and internal vapor-phase temperature under steady-state conditions were measured using the thermocouple placed on the outer wall and the radially movable thermocouple inside the heat pipe. The experimental results reveal that the vapor-phase temperature distribution is non-uniform in the radial direction on steady-state condition, exhibiting a certain thermal gradient. Different methods for selecting vapor temperatures, in combination with measured outer wall temperature, were employed to derive the experimental values of a_cc under different work conditions and operating temperatures based on the Hertz-Knudsen-Schrage equation. Analysis demonstrates a good linear relationship between the logarithmic value of a_cc and the logarithmic saturation pressure within the sodium heat pipe, which remains consistent for different sodium contents and inclination angles. However, when using the wall temperature of the adiabatic section or the vapor-phase temperature of the adiabatic section as the vapor temperature, a_cc tends to be relatively small due to the influence of radial thermal resistance and the wetting properties of liquid sodium, particularly below the wetting transition temperature (550 ℃), but it still satisfied a logarithmic linear relationship. Nevertheless, as the contact angle between the liquid sodium and the capillary wick approached 0°, the effect of the capillary wick became more pronounced, leading to a significant increase in a_cc due to the axial spreading facilitated by the excellent wetting properties of liquid sodium, therefore, the value of a_cc after the wetting contact angle transition temperature is also relatively larger. Overall, there is still a good linear relationship between the logarithmic value of a_cc and the logarithmic saturated vapor pressure. Finally, through fitting analysis, an empirical relationship for a_cc of sodium within the heat pipe at different temperatures was established, which can be used to predict a_cc under various operating conditions.