A　capillary　coating　with　a　photochromic　spiropyran　doped　polydimethylsiloxane　composite　for　HCl　vapor　detection　is　developed.　By　this　simple　method,　that　is,　by　the　waveguiding　capacity　of　capillary,　the　responsive　fluorescence　of　spiropyran　is　efficiently　collected　to　the　spectrometer.　A　rapid　sensing　as　short　as　5　s　to　sub-ppm　levels　HCl　vapor　concentration　(0.15-3　ppm)　is　achieved.　Furthermore,　the　UV-responsive　properties　of　spiropyran　doped　polydimethylsiloxane　composite　are　investigated.　Intriguingly,　a　wide　range　of　UV　intensity　(20　mu　W/cm(2)　to　1447　mu　W/cm(2))　is　able　to　be　linearly　responded　through　the　proposed　strategy.　This　method　does　not　need　complex　fabrication　processes　or　chemical　treatments　but　provides　a　robust　signal　and　rapid　response　for　small　acid　vapor　concentration　detection.　We　envision　that　this　research　may　enhance　the　potential　of　photochromism　for　applications　in　acid　vapor　sensing　and　UV　dosimeter.