Abstract: The liquid-metal heat pipe transient analysis code has been developed for the purpose of researching the startup characteristic of liquid-metal heat pipes from a frozen state. The code is capable of simulating the complex process of phase-change, the vapor flow and the transfer of mass and heat on liquid-vapor interface during startup. The pure-conduction model was used in pipe wall and porous wick region with the consideration of fusion/solidification and evaporation/condensation process. The dusty gas model was used to describe the various vapor flow regimes. Velocity and pressure of vapor were solved by the compressible SIMPLEC algorithm since the vapor was highly compressible during startup. The startup of a sodium heat pipe was simulated by using the code and the results were compared with experiment data. The results show that numerical results agree well with experiment data.