Abstract: The heat pipe cooling reactor is a type of small modular reactor that attracts attention due to its long-term life, high power density, ease of modular assembly, convenience and high heat transfer rates, which could be applied to dynamical systems such as the supply of electrical energy in space or the deep sea, among other areas. High temperature heat pipes, as key components of heat pipe cooling reactors, have significant engineering implications for understanding their heat transfer performance under various parameters. This study constructs a heat transfer performance model of alkali metal potassium high temperature heat pipes based on the computational fluid dynamics (CFD) method, thoroughly investigating the impact of different parameters on heat transfer performance. In present study, the volume of fluid (VOF) two-phase method was employed to model the complex phase change in high temperature heat pipe. The Lee model was simple to use and reflects the possible exchange of thermal mass at the phase interface or inside each phase. The thermal physical properties of liquid alkali metal potassium were added by user defined functions (UDFs) into CFD software based on the previous reference. In addition, the porous wick structure was considered as a homogeneous porous media for high temperature heat pipe. The different boundary conditions were set for three sections of outer wall surface of alkali metal potassium high temperature heat pipe. In comparing with the experiment, an alkali metal potassium heat pipe was fabricated. The same thermal-hydraulic condition was employed in present numerical model. The model was verified for accuracy by related experiment. The CFD results indicate that as the inclination angle increases, the wall temperature of the evaporation section rises. The equivalent thermal resistance decreases with inclination angle increasing, but the trend is not significant. With the developing of the filling ratio (FR), the equivalent thermal resistance continues to decline. At high FR condition, the equivalent thermal resistance varies at the critical inclination angle, significantly impacting the heat transfer performance. The findings of this study are of great importance for analyzing the heat transfer characteristics of alkali metal potassium high temperature heat pipes and optimizing design.