The　objective　of　this　work　is　to　study　the　flow　behavior　and　oil　film　thickness　in　the　vertical　helical　channel　to　improve　the　efficient　operation　of　the　single　screw　expander.　The　volume-of-fluid　(VOF)　model　is　adopted　to　examine　various　effects,　including　flow　direction,　oil　viscosity,　surface　tension,　flow　rate,　and　oil　inlet　width　on　the　liquid　film　thickness　distribution　and　liquid　holdup.　An　interesting　phenomenon　is　found　that　the　gas　axial　velocity　is　accelerated　in　the　flow,　and　this　has　a　profound　influence　on　the　liquid　film　thickness　distribution　and　liquid　holdup.　The　liquid　film　thickness　exhibits　a　significant　improvement　as　the　downward　flow　is　considered.　The　liquid　film　thickness　becomes　more　symmetrical　with　increasing　the　oil　viscosity,　surface　tension,　oil　flow　rate,　and　inlet　width,　and　more　liquid　are　concentrated　at　the　two　endpoints　of　the　channel.　A　higher　viscosity　oil　or　larger　surface　tension　coefficient　will　result　in　a　higher　liquid　holdup.　These　results　and　analysis　are　crucial　for　improving　the　performance　of　single　screw　expanders.