The structure and thermal stability of gold nanowire encapsulated in single-walled carbon nanotube (SWCNT) were studied by molecular dynamics simulations. A (8,8) SWCNT was used as a model system and the simulated annealing method was employed to find the stable structure of the gold nanowire at room temperature. Ourresults show that the gold nanowire encapsulated in a (8,8) SWCNT has a cylindrical shape and a helical shell structure. The helical-shell nanowire is thermally stable at temperatures much higher than the melting temperature of its bulk counterpart and is different from the gold nanowire formed in free space without the nanotube envelope. We also found that the spiral nanowire undergoes structural changes at higher temperatures.