A　mathematical　model　was　developed　to　investigate　the　two-component　mixture　spontaneous　condensation.　Numerical　simulations　were　performed　for　the　two-component　mixture　flow　in　Laval　nozzle.　The　comparison　between　numerical　and　the　experimental　results　shows　that　the　model　is　accurate.　The　influences　of　the　expansion　rate　of　the　nozzle　on　the　spontaneous　condensation　and　flow　characteristics　were　investigated.　It　was　found　that　under　the　same　conditions,　as　the　expansion　rate　increases,　the　Wilson　point　moves　to　the　inlet　side,　the　maximum　supercooling　and　the　nucleation　rate　and　the　droplet　number　also　increase,　the　mean　radius　of　the　liquid　droplets　decreases　and　the　vapor　in　the　mixture　reaches　its　supersaturated　state　earlier.　Copyright　©　2009　by　ASME.