By　using　a　self-designed　5.00-m-long　duct　with　a　cross-section　of　0.30　m　×　0.30　m,　a　seris　of　experiments　were　performed　on　premixed　hydrogen-air　gases　in　which　volume　fraction　of　hydrogen　was　30%.　And　the　effects　of　vent　burst　pressure　(pv)　on　the　flame　propagation　and　pressure-time　histories　in　the　duct　were　experimentally　iveatigated.　The　explosion　flames　were　recorded　by　a　high-speed　camera　at　a　frequency　of　2.5　kHz.　Five　piezoelectric　pressure　transducers　were　employed　to　record　the　internal　and　external　overpressure.　The　duct　had　been　evacuated　using　a　vacuum　pump　before　the　experiment,　and　the　premixed　hydrogen-air　gases　with　volume　fraction　of　30%　was　prepared　according　to　Dalton’s　law　of　partial　pressure.　The　variation　of　the　vent　burst　pressure　was　achieved　by　changing　the　thickness　of　the　aluminum　foil　which　was　used　as　vent　cover.　The　results　show　that　the　first　three　stages　of　the　flame　structure　in　the　duct　are　hemispherical,　finger-shaped　and　tulip　flame,　respectively.　pv　has　a　significant　effect　on　the　structure　of　tulip　flame　and　its　subsequent　development.　Three　pressure　peaks　(pb,　pout,　pext)　can　be　distinguished　from　the　pressure-time　histories　monitored　by　the　pressure　transducer　near　the　vent,　corresponding　to　three　different　generation　mechanisms:　burst　of　the　aluminum　film,　venting　of　burned　mixtures,　and　the　external　explosion,　respectively.　The　three　pressure　peaks　increase　with　an　increase　in　pv.　pb　is　the　dominant　pressure　peak　in　most　cases.　The　maximum　internal　overpressure　increases　as　pv　increases,　and　the　position　where　the　maximum　internal　overpressure　was　measured　depended　on　pv.　The　maximum　internal　overpressure　was　obtained　at　the　center　of　the　duct　(PT2)　when　pv≤42　kPa,　but　near　the　open　end　of　the　duct　(PT3)　if　pv＞42　kPa.　When　the　flame　reached　the　vent,　it　ejected　from　the　vent　and　then　ignited　the　external　combustible　cloud.　Therefore,　the　external　explosion　is　triggered.　pv　significantly　affects　the　flame　evolution　outside　the　duct,　but　there　is　no　significant　difference　in　the　maximum　length　of　the　external　flame　at　various　pv.　A　non-monotonic　trend　between　the　maximum　external　overpressure　and　pv　was　observed.　©　2023　Explosion　and　Shock　Waves.　All　rights　reserved.