Dichloromethane　(DCM),　which　is　a　widely　used　organic　solvent　in　industrial　production,　is　currently　classified　as　a　Class　2A　carcinogen.　Considering　its　potential　harm　to　human　health,　it　is　necessary　to　design　a　convenient　and　economical　method　to　monitor　the　concentration　of　DCM　in　the　environment　in　real　time.　Here,　we　present　a　visualized　fluorescence　sensor　for　DCM　utilizing　photochromic　CsPbBr3　perovskite　nanocrystals　(PNCs).　By　measuring　the　amount　of　chloride　ions　dissociated　from　DCM　under　365　nm　UV　light　catalysis,　the　resulting　ion　exchange　products　of　CsPbBr3-xClx　exhibit　distinct　fluorescence　colors　based　on　the　halogen　ratio,　enabling　visual　detection.　In　addition,　we　have　observed　a　linear　relationship　between　the　concentration　of　DCM　and　the　wavelength　shift　difference　of　PNCs　after　a　30　min　365　nm　UV　exposure,　within　the　DCM　concentration　range　of　1-20%　(0.16-3.11　mM).　And　the　limit　of　detection　was　calculated　to　be　0.29%.　We　have　successfully　utilized　this　sensor　to　detect　the　concentration　of　DCM　in　laboratory　waste　liquid,　achieving　a　high　recovery　rate.　This　application　is　beneficial　for　long-term　laboratory　personnel　to　promptly　identify　the　source　of　harmful　gases,　thereby　significantly　contributing　to　the　maintenance　of　laboratory　safety　and　physical　health.　©　2024　American　Chemical　Society.