Airborne　pollution,　derived　from　tiny　particulate　matter　(PM)　and　the　pandemic　virus,　strongly　stimulates　the　demand　for　personal　protective　materials　but　also　causes　serious　environmental　issues　due　to　the　mass　discarding　of　disposable　nondegradable　face　masks.　Despite　a　few　reports　of　bio-based　filters,　however,　it　remains　a　challenge　to　develop　biodegradable　respirators　with　efficient,　wet-stable　PM0.3　filtration　and　low　pressure　drop.　Herein,　the　degradable　multi-scale　fibrous　filter　composed　of　polylactic　acid　(PLA)　micro-/submicron-fibers　and　bacterial　cellulose　(BC)　nanofibers　was　rationally　designed　to　balance　the　filtration　efficiency　and　resistance.　The　2D　BC　nano-mesh　with　the　small　pores　was　self-assembled　by　the　electro-spraying　technique　and　the　PLA　submicron-fibrous　networks　with　medium　pores　were　prepared　by　the　electrospinning　technology.　The　multilayer　micro-/submicron-/nano-fiber　construction　endowed　the　membrane　with　a　low　pore　size　of　1.27　mu　m　and　also　extended　the　particle　flow　path,　which　contributed　to　the　efficient　and　durable　PM0.3　interception.　As　a　result,　the　prepared　filter　showed　over　99.89%　PM0.3　filtration　efficiency　but　a　low　pressure　drop　of　104　Pa.　More　significantly,　it　still　presented　over　99.68%　PM0.3　removal　after　long-term　filtration　under　90%　RH.　This　work　may　provide　meaningful　guidance　for　the　development　of　biodegradable　high-protective　air　filters.