Conventional　membrane　processes,　e.g.,　microfiltration　and　ultrafiltration,　suffer　from　severe　permeation　flux　decline　and　fouling　during　the　oily　wastewater　treatment.　The　superhydrophilic　surface　decoration　provides　an　important　and　effective　strategy　to　address　this　challenge.　Herein,　a　surperhydrophilic/underwater　superoleophobic　nanocomposite　surface　with　the　photocatalytic　properties　was　constructed　via　one-step　facile　vacuum-assisted　filtration　of　a　g-C3N4　nanosheet/SiO2　nanoparticle　dispersion　onto　a　microfiltration　membrane　substrate.　Specifically,　with　the　intercalation　of　20　mg.L-1　SiO2　nanoparticles　into　the　g-C3N4　nanosheets,　the　g-C3N4/SiO2　composite　membrane　showed　the　superhydrophilic/underwater　superoleophobic　properties　with　an　underwater　oil　contact　angle　of　170.0　+/-　0.3　degrees.　Such　a　g-C3N4/SiO2　composite　membrane　yielded　a　permeation　flux　of　＞1290　LMH.bar(-1)　with　an　oil　rejection　of　＞99.91%　during　the　vacuum　filtration　of　oil-in-water　emulsions.　The　g-C3N4/SiO2　composite　membrane　significantly　outperformed　the　pristine　microfiltration　substrate　that　had　severe　fouling　caused　by　oil　blockage.　Additionally,　the　g-C3N4/SiO2　composite　membrane　not　only　effectively　retained　the　E.　coli　bacteria　through　size　exclusion　effect,　but　also　promoted　the　inactivation　of　bacteria　via　visible-light　photocatalysis.　Therefore,　our　membrane　has　a　great　promise　in　practical　oily　wastewater　treatment　due　to　its　excellent　separation　performance　and　biofouling　resistance.