In　recent　years,　lead　halide　perovskite　nanocrystals　(PNCs)　have　presented　potential　scalable　applications　in　all　fields　due　to　their　outstanding　properties.　However,　most　commonly　used　PNCs　capped　with　oleic　acid　(OA)　and　oleylamine　(OAm)　suffer　from　bad　stability　in　polar　solutions　and　thus　require　various　surface　protections　with　organic　or　inorganic　materials.　Encapsulation　with　highly　hydrophobic　polystyrene　(PS)　is　one　of　the　most　efficient　ways　to　protect　PNCs;　however,　the　presently　used　swelling-shrinking　strategy　faces　several　challenges,　such　as　weak　interaction　between　PS　chains　and　the　surface　ligands　in　nonpolar　media　causing　a　low　encapsulation　efficiency,　and　serious　aggregation　of　PS　particles　during　the　shrinkage　process　leading　to　very　different　particle　sizes.　Herein,　alcohol-stable　polyacrylic　acid-capped　CsPbBr3　PNCs　(i.e.,　PAA-PNCs)　are　first　synthesized　and　then　in　situ　encapsulated　with　PS　shells　by　polymerizing　styrene　monomer　on　the　PNC　surfaces　in　a　polar　organic　solvent　(e.g.,　ethanol).　The　in　situ　PS-encapsulated　PAA-PNCs　(i.e.,　PAAPNCs@iPS)　exhibit　outstanding　monodispersity,　remarkable　water,　heat,　and　UV　stability,　high　fluorescence　activity,　and　color　purity.　The　unique　synthesis　strategy　and　good　performances　of　PAA-PNCs@iPS　will　boost　the　applications　of　PNCs　in　LEDs,　biological　imaging,　and　chemosensing.