With　the　accelerated　development　of　global　industrialization,　environmental　issues,　such　as　airborne　and　water　pollution　caused　by　suspended　solid　particulate　matter　(PM)　seriously　endanger　ecosystems　and　human　health.　Fibrous　filtration　and　separation　membranes　provide　an　effective　approach　to　pollution　treatment,　yet　they　still　face　challenges　in　efficient　and　high-flux　purification　of　highly　permeable　ultrafine　particles.　Herein,　an　ultrafine　nanofiber-based　membrane　with　rational　hierarchical　networks　is　designed　for　both　air　and　water　filtration.　Through　the　proposed　jet　branching　electrospinning　strategy,　a　multiscale　fiber　membrane　consisting　of　ultrafine　nanofibers,　medium　fibers,　and　coarse　submicron　fibers　is　prepared.　It　possesses　the　merits　of　ultrafine　fiber　diameter,　ultralow　pore　size,　high　specific　surface　area,　and　unique　hybrid　structure.　Benefiting　from　these　features,　the　obtained　multiscale　fibrous　filter　shows　superior　PM0.3　air　filtration　performance　(99.96%　PM0.3　removal,　low　pressure　drop　of　89　Pa)　and　water　filtration　capacity　(ultrafine　particle　rejection　efficiency　of　99.50%,　water　flux　of　9028.84　L　m-2　h-1).　Moreover,　the　controllable　structure　of　a　multiscale　fiber　filter　also　endows　itself　with　stable　and　durable　filtration　capacity.　This　work　may　provide　meaningful　references　for　the　development　of　high-performance　filtration　and　separation　materials.