The　rapid　maturation　of　the　gravity-driven　membrane　(GDM)　process　for　manganese　removal　from　surface　water　is　critical　to　its　practical　application.　In　this　study,　KMnO4　and　NaClO　were　used　to　investigate　their　effects　on　the　start-up　period　of　the　GDM　process　for　treating　manganese-containing　surface　water.　The　start-up　period　of　the　GDM　system　with　KMnO4　(24　days)　was　shorter　compared　to　that　with　NaClO　(40　days).　After　the　addition　of　KMnO4　and　NaClO,　the　stable　flux　of　the　GDM　system　was　significantly　improved,　and　the　bio-cake　layer　became　more　porous,　which　was　ascribed　to　the　reduction　of　proteins　in　the　extracellular　polymeric　substances　(EPS).　The　active　manganese　oxide　(MnOx)　in　the　bio-cake　layer　was　identified　as　delta-MnO2.　The　addition　of　the　oxidants　increased　the　proportion　of　Mn(III)　with　high　catalytic　oxidation　activity　in　delta-MnO2,　where　the　assisted　effect　of　KMnO4　(43.7%)　was　superior　to　that　of　NaClO　(27.8%).　The　development　of　delta-MnO2　in　the　natural　filtration　state　was　ascribed　to　the　enrichment　of　manganese　oxidizing　bacteria　(MnOB).　The　biological　action　only　accounted　for　9.4%-12.3%　of　the　manganese　removal　and　was　not　dominant.　The　difference　in　the　start-up　period　of　the　GDM　process　was　dependent　on　the　autocatalytic　oxidation　of　Mn(III)　in　delta-MnO2　in　the　bio-cake　layer.　These　findings　provided　acceptable　and　practical　strategies　for　the　rapid　and　safe　manganese　removal　in　the　GDM　process.