All-inorganic　perovskites　have　emerged　in　the　field　of　optoelectronic　devices　for　their　excellent　light　absorption　and　energy　conversion　efficiencies,　as　well　as　their　superior　stability　compared　to　organic-inorganic　perovskites.　The　two-dimensional　(2D)　all-inorganic　perovskites　have　a　higher　exciton　binding　energy　and　carrier　recombination　efficiency　than　their　bulk　counterparts　due　to　the　quantum　confinement　effect,　which　indicts　high　strong　light-matter　interactions　and　is　suitable　for　special　integrated　optoelectronics　such　as　a　micro　laser　or　quick-response　photodetector.　However,　it　is　difficult　to　fabricate　a　2D　large-sized　sample　with　high　crystal　quality　due　to　the　nonlayered　structure,　which　limits　its　further　research　and　practical　application.　In　this　work,　based　on　an　atmospheric　pressure　chemical　vapor　deposition　strategy　combining　a　space-confined　method　and　van　der　Waals　epitaxy,　the　synergistic　effect　of　these　two　techniques　results　in　large-sized　ultrathin　all-inorganic　CsPbI3　perovskite　nanosheets　for　which　the　lateral　dimension　can　exceed　50　mu　m　while　the　smallest　thickness　can　reach　3　nm.　The　high　crystal　quality　of　the　square-like　samples　has　been　confirmed　by　a　microstructure　characterization,　while　the　corresponding　performances　like　long　carrier　life　(360　ns),　high　resistivity,　and　good　stability　were　also　verified,　implying　great　promise　for　their　applications　in　high-performance　integrated　optoelectronics.　This　method　may　pave　the　way　for　a　uniform　fabrication　of　other　2D　nonlayered　materials　as　well.