The　film　flow　behavior　in　an　oil-gas　cyclone　separator　was　experimentally　studied　to　improve　the　separation　efficiency　in　terms　of　the　effect　of　the　oil　film　on　the　cylinder　wall.　The　oil　film　flow　pattern　was　captured　using　a　high-speed　camera,　and　the　cylinder　wall　was　divided　into　seven　regions　to　analyze　according　to　the　different　oil　film　flow　patterns.　Along　the　cyclone　cylinder　height,　the　central　part　of　the　cylinder　was　the　main　flow　area,　in　which　droplet-wall　collisions　and　oil　film　splashing　were　severe.　Additionally,　the　oil　film＇s　distribution　characteristics　under　inlet　velocities　of　14.0,　16.0,　and　18.0　m/s　were　compared,　and　the　results　showed　that　more　splashing　oil　droplets　were　generated　under　higher　inlet　velocity.　Moreover,　changing　the　structure　of　the　central　channel　and　outer　cylinder　slightly　changed　the　oil　film＇s　area　and　flow　pattern　but　exhibited　a　weak　effect　on　the　oil　film　thickness　and　re-entrainment.　Then,　an　improved　structure　was　proposed　by　adding　a　porous　cylinder　to　the　outer　cyclone　to　avoid　the　generation　of　small　splashing　droplets　from　the　oil　film.　The　performance　of　the　modified　separator　was　measured　in　a　real　oil-injected　compressor　system,　which　demonstrated　higher　separation　efficiency　with　no　increase　in　static　pressure　loss.　The　separation　efficiency　increased　by　up　to　2.7%,　while　the　pressure　loss　decreased　by　up　to　10%.　Thus,　the　improved　structure　can　improve　the　performance　of　oil-gas　separators　by　changing　the　distribution　and　thickness　of　the　oil　film　on　the　cylinder　wall.