The　gravity-driven　membrane　(GDM)　system　is　an　energy-efficient　and　environmentally　sustainable　water　purification　process;　however,　after　prolonged　operation,　its　membrane　flux　remains　relatively　low,　making　it　necessary　to　adopt　effective　strategies　for　improving　system　performance.　In　this　study,　the　effects　of　hydrostatic　pressure　(60,　100,　200　mbar)　and　pre-coating　with　aluminum-based　flocs　(ABF)　on　GDM　flux　and　organic　matter　removal　were　investigated,　and　the　regulatory　mechanisms　of　the　bio-cake　layer　were　explored　through　interactions　between　morphological　structure,　composition　and　microbes.　The　results　showed　that　the　stable　flux　of　the　GDM-ABF　system　at　a　hydrostatic　pressure　of　60　mbar　was　almost　equal　to　that　at　100　mbar,　and　it　outperformed　higher　hydrostatic　pressure　in　organic　matter　removal,　resulting　in　a　more　porous　bio-cake　layer　structure.　GDM-ABF　system　at　60　mbar　achieved　38.51%　energy　saving　compared　to　that　at　100　mbar.　Increased　hydrostatic　pressure　led　to　a　denser　biofouling　layer　and　higher　EPS　concentrations,　whereas　pre-coating　reduced　the　EPS　concentration　and　resulted　in　a　looser　biofouling　layer.　Hydrostatic　stress　and　pre-coating　determined　membrane　fouling　by　regulating　microbial　communities　and　key　metabolites.　Increasing　hydrostatic　pressure　down-regulated　arginine　and　proline　metabolism　and　aggravated　membrane　fouling,　while　pre-coating　ABF　up-regulated　arginine　and　proline　metabolism,　down-regulated　galactose　metabolism,　and　alleviated　the　membrane　fouling.　Hydrostatic　stress　and　pre-coating　altered　the　abundance　of　keystone　species　involved　in　extracellular　polymeric　substances　(EPS)　formation　within　the　bio-cake　layer.　Pre-coating　with　ABF　at　low　hydrostatic　pressure　can　achieve　stable　flux　and　effective　water　purification　in　GDM　systems,　similar　to　high　hydrostatic　pressure　conditions,　with　the　added　benefits　of　being　more　environmentally　friendly　and　low-carbon.　This　study　proposes　a　strategy　to　balance　flux　and　energy　consumption　in　GDM　systems,　providing　theoretical　and　technical　support　for　the　efficient　application　of　GDM　technology　in　membrane　water　treatment　processes.　©　2024　Elsevier　Ltd