A　hybrid　model　that　combines　first　principles　calculations　and　thermodynamic　evaluation　was　developed　to　describe　the　thermal　stability　of　a　nanocrystalline　solid　solution　with　weak　segregation.　The　dependence　of　the　solute　segregation　behavior　on　the　electronic　structure,　solute　concentration,　grain　size　and　temperature　was　demonstrated,　using　the　nanocrystalline　Cu-Zn　system　as　an　example.　The　modeling　results　show　that　the　segregation　energy　changes　with　the　solute　concentration　in　a　form　of　nonmonotonic　function.　The　change　in　the　total　Gibbs　free　energy　indicates　that　at　a　constant　solute　concentration　and　a　given　temperature,　a　nanocrystalline　structure　can　remain　stable　when　the　initial　grain　size　is　controlled　in　a　critical　range.　In　experiments,　dense　nanocrystalline　Cu-Zn　alloy　bulk　was　prepared,　and　a　series　of　annealing　experiments　were　performed　to　examine　the　thermal　stability　of　the　nanograins.　The　experimental　measurements　confirmed　the　model　predictions　that　with　a　certain　solute　concentration,　a　state　of　steady　nanograin　growth　can　be　achieved　at　high　temperatures　when　the　initial　grain　size　is　controlled　in　a　critical　range.　The　present　work　proposes　that　in　weak　solute　segregation　systems,　the　nanograin　structure　can　be　kept　thermally　stable　by　adjusting　the　solute　concentration　and　initial　grain　size.