The　H2/O2　internal　combustion　is　promising　to　be　adopted　as　auxiliary　power　by　combusting　the　wasted　hydrogen　in　the　upper　stages　under　aerospace　conditions.　Concerning　no　inert　gases　participating　the　combustion,　the　control　of　H2/O2　heat　release　is　a　great　challenge.　This　paper　proposes　to　control　the　heat　release　by　adopting　an　active　pre-chamber　(PC).　All　the　combustion　consumed　oxygen　is　injected　into　the　PC.　The　combustion　of　oxygen　and　small　amount　of　pre-existed　H2　in　PC　increases　the　PC　pressure,　enabling　the　hot　reactant　and　massive　oxygen　to　be　injected　into　the　main　chamber　(MC)　to　arrange　the　oxygen　jet　induced　hydrogen　diffusive　combustion.　The　test　was　conducted　on　a　constant　volume　combustion　bomb　(CVCB)　to　explore　the　effects　of　equivalence　ratio　(φG)　and　orifice　diameter　on　the　diffusive　H2/O2　combustion　characteristics.　The　results　showed　that　increasing　φG　resulted　in　the　decreased　premix　combustion　fraction　and　prolonged　combustion　duration.　The　peak　pressure　of　MC　dropped　with　φG　indicating　the　ability　of　adjusting　engine　load　by　varying　φG.　The　heat　release　process　could　be　controlled　either　by　φG　or　orifice　diameter.　Properly　increasing　the　orifice　diameter　availed　shortening　the　combustion　duration　and　promoting　the　heat　release　efficiency.　©　2024　Elsevier　Ltd