A　mathematical　model　was　developed　to　investigate　the　water　vapor　spontaneous　condensation　under　supersonic　flow　conditions.　A　numerical　simulation　was　performed　for　the　water　vapor　condensable　supersonic　flows　through　Laval　nozzles　under　different　flow　friction　conditions.　The　comparison　between　numerical　and　experimental　results　shows　that　the　model　is　accurate　enough　to　investigate　the　supersonic　spontaneous　condensation　flow　of　water　vapor　inside　Laval　nozzles.　The　influences　of　flow　friction　drag　on　supersonic　spontaneous　condensation　flow　of　water　vapor　inside　Laval　nozzles　were　investigated.　It　was　found　that　the　flow　friction　has　a　direct　effect　on　the　spontaneous　condensation　process　and　therefore　it　is　important　for　an　accurate　friction　prediction　in　designing　this　kind　of　Laval　nozzles.