Low　temperature　at　the　outlet　of　drilling　bit　nozzles　can　be　induced　due　to　Joule-Thomson　effect　during　well　drilling　using　gases　as　drilling　fluid.　In　this　study,　a　numerical　simulation　model　for　analyzing　the　temperature　distribution　around　the　bottom　of　the　hole　was　established　based　on　the　Joule-Thomson　cooling　effect,　and　then　the　induced　thermal　shock　stress　was　calculated　according　to　the　temperature　distribution.　The　expansion　and　instability　of　rock　cracks　were　analyzed　in　terms　of　a　stress　intensity　factor　at　the　cracking　tips　of　rock.　Experiments　were　conducted　using　liquid　nitrogen　for　cooling　of　rock　samples　in　order　to　verify　the　thermal　cracking　models,　and　a　real-time　acoustic　technique　was　used　to　measure　the　cracking　effect.　The　results　show　that,　under　the　thermal　stress,　a　minimal　cracking　resistance　of　anti-propagation　exists,　and　cuttings　with　small　sizes　were　obtained　during　gas　drilling.　It　appears　that　the　wave　velocity　decreases　at　low　temperatures,　and　the　first　wave　amplitude　has　a　dramatic　delay,　which　illustrate　that　the　cooling　can　have　an　important　impact　on　the　internal　structure　of　rocks.　©　2016,　Periodical　Office　of　China　University　of　Petroleum.　All　right　reserved.