A　dual-precursors　co-pyrolysis　strategy　was　adopted　to　prepare　photocatalysts　of　MoO3/g-C3N4　composite　from　MoS2/melamine　through　a　facile　one-pot　method.　By　following　this　strategy,　MoS2　was　in-situ　transformed　to　MoO3　accompanying　with　the　pyrolysis　and　polymerization　of　melamine　to　g-C3N4　nanosheets.　A　set　of　samples　about　MoO3/g-C3N4　composite　containing　different　MoO3　contents　were　prepared　and　the　visible-light　driven　photocatalytic　performance　of　samples　were　investigated.　The　photocatalytic　activity　was　notably　enhanced　and　the　highest　evolution　rate　for　H2　reached　13.9　times　and　2.5　times　that　of　the　pristine　g-C3N4　and　the　MoO3/g-C3N4　derived　from　MoO3/melamine,　respectively.　On　the　one　hand,　layered　MoS2　used　as　the　precursor　of　MoO3　contributed　to　the　intimate　contact　with　g-C3N4　nanosheets　and　the　high　dispersity　of　derived　MoO3,　and　on　the　other　hand,　the　morphology　and　electronic　structure　of　g-C3N4　were　actually　changed　by　the　strong　interaction　between　the　MoO3　and　g-C3N4,　thus　inducing　an　efficient　Z-scheme　(S-scheme)　system　in　the　composite.　The　above-mentioned　co-operation　effect　in　the　composite　resulted　in　the　significant　improvement　on　the　activity　of　photocatalytic　H2　evolution.　This　work　presented　a　valuable　reference,　by　taking　MoO3/g-C3N4　as　an　example,　for　the　construction　of　composite-photocatalyst　system　in　visible-light-driven　H2　evolution.　©　2020　Hydrogen　Energy　Publications　LLC