Hydrogen　production　by　supercritical　water　gasification　of　biomass　has　broad　application　prospects.　The　migration　and　regulation　mechanism　of　nitrogen　in　supercritical　water　is　one　of　the　key　issues　in　biomass　utilization.　As　a　nitrogen-containing　model　compound　of　biomass,　indole　was　used　to　study　the　mechanism　of　nitrogen　migration　during　supercritical　water　gasification　from　a　molecular　perspective　by　using　reactive　empirical　force　fields　(Reaxff)　combined　with　Density　functional　theory　(DFT)　method.　The　pyrrole　ring　cracking　was　the　first　stage　and　then　most　of　the　nitrogen　atoms　left　the　carbon　skeleton　to　form　ammonia　precursor　radicals　after　being　attacked　by　H　or　OH　free　radicals　in　supercritical　water.　The　overall　activation　energy　of　each　pyrrole　ring　opening　way　was　calculated.　The　dominant　way　for　pyrrole　ring　opening　was　analyzed　and　the　competitive　relationship　among　the　different　ring-opening　ways　was　specified　by　comparing　the　activation　energies　of　transition　states　and　relative　energies　of　intermediates.　Compared　with　pyrolysis　conditions,　supercritical　water　molecules　greatly　promoted　the　separation　of　nitrogen　atoms　from　the　carbon　skeleton　to　form　NH3　and　inhibited　the　formation　of　HCN.　The　higher　temperature　could　facilitate　the　indole　conversion　and　the　hydrogen　generation,　but　it　also　increased　the　possibility　of　char　formation,　causing　part　of　the　nitrogen　to　re-enter　the　organic　structure.　This　study　revealed　the　mechanism　from　the　view　of　microscopic　atoms,　and　provided　theoretical　support　for　the　nitrogen　regulation　in　supercritical　water　gasification　of　biomass.　©　2020　Elsevier　B.V.