The　factors　contributing　to　high　penetration　rate　of　gas　drilling　are　complex.　The　isentropic　flow　is　generated　when　gas　passes　through　bit　nozzle　during　gas　drilling.　This　phenomenon　will　lead　to　cryogenic　effects,　and　then　the　resulted　thermal　shock　stress　at　bottom　hole　rock　will　reduce　the　rock　strength,　contributing　to　the　role　of　the　rock　failure.　First,　a　model　for　the　temperature　distribution　of　bottom　hole　rock　under　asymmetric　cooling　is　established.　The　three-dimensional　dynamic　thermal　shock　stress　distribution　model　is　established　based　on　the　temperature　field.　Then,　the　change　of　the　rock　cohesion　is　analyzed　by　using　the　Mohr-Coulomb　criterion.　The　results　demonstrate　that　as　the　temperature　decreases,　the　strength　of　rock　is　greatly　reduced,　resulting　in　increased　ROP.　Finally　the　liquid　nitrogen　cooling　tests　and　real-time　measurements　of　acoustic　waves　are　conducted　to　verify　the　above　theory.　The　first　wave　amplitude　has　a　dramatic　delay,　which　illustrates　that　the　cooling　has　an　important　impact　on　the　internal　structure　of　rock.　The　mechanism　of　rock　failure　under　dynamic　low　temperature　in　gas　drilling　is　clearly　depicted.　©　2016,　Editorial　Office　of　Chinese　Journal　of　Geotechnical　Engineering.　All　right　reserved.