The　thermo-stability　and　unfolding　behaviors　of　a　small　hyperthermophilic　protein　Sso7d　as　well　as　its　single-point　mutation　F31A　are　studied　by　molecular　dynamics　simulation　at　temperatures　of　300　K,　371　K　and　500　K.　Simulations　at　300　K　show　that　the　F31A　mutant　displays　a　much　larger　flexibility　than　the　wild　type,　which　implies　that　the　mutation　obviously　decreases　the　protein＇s　stability.　In　the　simulations　at　371　K,　although　larger　fluctuations　were　observed,　both　of　these　two　maintain　their　stable　conformations.　High　temperature　simulations　at　500　K　suggest　that　the　unfolding　of　these　two　proteins　evolves　along　different　pathways.　For　the　wild-type　protein,　the　C-terminal　alpha-helix　is　melted　at　the　early　unfolding　stage,　whereas　it　is　destroyed　much　later　in　the　unfolding　process　of　the　F31A　mutant.　The　results　also　show　that　the　mutant　unfolds　much　faster　than　its　parent　protein.　The　deeply　buried　aromatic　cluster　in　the　F31A　mutant　dissociates　quickly　relative　to　the　wild-type　protein　at　high　temperature.　Besides,　it　is　found　that　the　triple-stranded　anti-parallel　beta-sheet　in　the　wild-type　protein　plays　an　important　role　in　maintaining　the　stability　of　the　entire　structure.