With　its　charged　property　and　multifunctional　merit,　polyelectrolyte　multilayer　(PEM)　membrane　shows　great　promise　in　water　purification.　However,　the　time-consumption　fabrication　and　dense　microstructure　of　PEM　membrane　hamper　the　development　of　high-performance　PEM　membrane　for　wastewater　treatment.　In　this　work,　we　propose　the　dynamic　self-assembly　coupled　ice-templating　technique　to　fabricate　loose　nanofiltration　membrane　in　a　rapid　speed.　By　vacuum-assisted　filtration,　poly(ethyleneimine)　(PEI)　and　sodium　alginate　(SA)　can　be　rapidly　assembled　into　and　onto　porous　ceramic　tube,　which　was　subsequently　experienced　freeze-drying　to　tailor　the　microstructure　of　the　result　PEM　membrane.　The　microstructure　variation　was　approved　by　low-field　nuclear　magnetic　resonance.　After　further　chemical　crosslinking,　the　prepared　loose　PEM　nanofiltration　membrane　offers　a　superior　water　permeability　of　57.4　LMH/bar,　dye　rejection　efficiency　of　＞99%,　and　low　rejection　to　salts　(12.1%　for　NaCl),　as　well　as　long-term　stability,　which　can　thus　be　potentially　applied　for　clean　water　harvesting　from　dyestuff　wastewater.　The　method　we　proposed　opens　a　new　door　to　intensify　the　mass　transfer　of　water　through　the　membrane　for　high-performance　membrane　development.