2,6-bis(picrylamino)-3,5-dinitropyridine(PYX)has　excellent　thermostability,which　makes　its　thermal　decomposition　mechanism　receive　much　attention.In　this　paper,the　mechanism　of　PYX　thermal　decomposition　was　investigated　thoroughly　by　the　ReaxFF-Ig　force　field　combined　with　DFT-B3LYP(6-311++G)method.The　detailed　decomposition　mechanism,small-molecule　product　evolution,and　cluster　evolution　of　PYX　were　mainly　analyzed.In　the　initial　stage　of　decomposition,the　intramolecular　hydrogen　transfer　reaction　and　the　formation　of　dimerized　clusters　are　earlier　than　the　denitration　re-action.With　the　progress　of　the　reaction,one　side　of　the　bitter　amino　group　is　removed　from　the　pyridine　ring,and　then　the　pyridine　ring　is　cleaved.The　final　products　produced　in　the　thermal　decomposition　process　are　CO2,H2O,N2,and　H2.Among　them,H2O　has　the　earliest　generation　time,and　the　reaction　rate　constant(k3)is　the　largest.Many　clusters　are　formed　during　the　decomposition　of　PYX,and　the　formation,aggregation,and　decomposition　of　these　clusters　are　strongly　affected　by　temperature.At　low　temperatures(2500　K-2750　K),many　clusters　are　formed.At　high　temperatures(2750　K-3250　K),the　clusters　aggregate　to　form　larger　clusters.At　3500　K,the　large　clusters　decompose　and　become　small.In　the　late　stage　of　the　reaction,H　and　N　in　the　clusters　escaped　almost　entirely,but　more　O　was　trapped　in　the　clusters,which　affected　the　auto-oxidation　process　of　PYX.PYX＇s　initial　decomposition　activation　energy(Ea)was　calculated　to　be　126.58　kJ/mol.This　work　contributes　to　a　theoretical　understanding　of　PYX＇s　entire　thermal　decomposition　process.