Abstract: To analyze the effect of the cone angle on the performance of the evaporator in vapor-anode Alkali Metal Thermal to Electric Converter (AMTEC), a steady-state two-dimensional thermal hydraulic model for liquid-return wick and conical evaporator was developed. The effects of different cone angles on the surface temperature distribution, void fraction and capillary limit of the evaporator under different operating conditions were studied. The results showed that the evaporation area and vapor pressure along the surface of the conical evaporator were larger than those of the plane evaporator, and the surface vapor pressure of the conical evaporator with 15° cone angle was 35.29 kPa, 1.62 kPa higher than that of the plane evaporator, at cold end temperature of 623 K, hot end temperature of 1123 K and electrical current of 2.5 A. However, the capillary limited domain of the deep cone evaporator was larger than that of the shallow cone evaporator, and it was more likely to experience large area condensation at the center of the evaporator surface. 15° conical evaporator experienced condensation 7%~18% of its surface, at electrical current of 1~2 A. Therefore, the shallow cone evaporator was recommended for the vapor-anode AMTEC.