The　pressure　history　in　the　explosion　syngas/air　mixtures　with　H2O　addition　over　a　wide　range　of　equivalence　ratios　at　elevated　temperatures　was　recorded　to　study　the　explosion　characteristics　in　a　constant　volume　confined　vessel.　CO　mole　fractions　in　syngas　are　from　0.5　to　0.95,　initial　temperatures　are　from　373　K　to　473　K,　and　H2O　addition　ratios　are　from　0　to　30%.　The　explosion　parameters　such　as　explosion　pressure,　explosion　time,　maximum　rate　of　pressure　rise,　and　deflagration　index　are　obtained　from　the　experiment.　Effects　of　the　equivalence　ratio,　initial　temperature,　CO/H-2　ratio　and　dilution　ratio　on　the　explosion　parameters　are　examined.　These　parameters　are　important　input　properties　for　evaluation　of　hazards　of　the　explosion　and　the　design　the　combustion　vessel.　In　addition,　the　adiabatic　explosion　pressure　is　also　calculated　assuming　the　flame　propagation　is　a　constant-volume　and　adiabatic　process.　Results　show　the　experimentally　determined　normalized　explosion　pressure　and　the　normalized　adiabatic　explosion　pressure　show　different　trends　with　the　increase　of　CO/H-2　ratio.　The　experimental　determined　normalized　explosion　pressure　decreases　but　normalized　adiabatic　explosion　pressure　increases　with　the　increase　of　CO/H-2　ratio　in　the　syngas　mixture.　This　is　mainly　because　the　heat　loss　is　larger　for　the　mixture　with　a　higher　CO/H-2　ratio.　At　last,　the　heat　loss　during　the　combustion　process　was　calculated　by　the　difference　between　experimental　and　adiabatic　explosion　pressure.　With　the　addition　of　CO　dilution　ratio　in　the　mixture,　the　amount　of　heat　loss　transferred　to　the　wall　heat　loss　to　the　unit　area　increases　greatly.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.