Pervaporation　has　great　potential　in　the　separation　of　many　significant　mixtures.　However,　excessive　penetration　of　separation　layer　into　the　substrate　pores　enhances　the　transport　resistance　of　solvent　molecules,　which　impedes　the　development　of　pervaporation　membrane.　In　this　study,　a　facile　floating-on-water　(FOW)　method　was　used　to　prepare　poly(dimethylsiloxane)　(PDMS)/polytetrafluoroethylene　(PTFE)　composite　membranes.　The　formation　of　separation　layer　and　preparation　of　composite　membrane　were　step-by-step　completed　through　this　liquid-liquid　interface　induced　method.　The　PDMS　layer　thickness　could　be　precisely　regulated　from　0.5　to　8　mu　m.　Moreover,　the　pore　penetration　could　be　controlled　by　optimizing　pre-crosslinking　density,　crosslinking　time　on　water　and　polymer　solution　volume.　The　obtained　PDMS/PTFE　composite　membrane　exhibited　a　high　flux　of　2016　g　center　dot　m(-2)center　dot　h(-1)　with　the　separation　factor　of　12　when　separating　ethanol　from　a　5　wt%　ethanol/water　mixture.　The　performance　of　the　membrane　could　be　stable　for　over　200　h,　exhibiting　great　potential　in　ethanol　perm-selective　pervaporation.