As　a　highly　active　free　radical　in　vivo,　peroxynitrite　can　damage　various　biological　macromolecules　and　cause　a　series　of　major　diseases,　which　is　of　great　significance　to　determine　its　content　and　reactive　mechanism.　It　is　very　difficult　to　capture　the　dynamic　process　of　peroxynitrite　due　to　its　active　property　and　fast　reacted　rate.　In　this　paper,　we　firstly　explored　the　kinetic　characteristics　of　peroxynitrite　and　tyrosine　with　the　presence　of　Hemoglobin　and　Hemin　by　using　flow　injection　analyzer.　The　results　showed　that　the　oxidation　processes　of　peroxynitrite　and　tyrosine　catalyzed　with　hemoglobin　and　hemin　were　in　accordance　with　Michaelis-Menten＇s　dynamics　law;　Based　on　the　Michaelis　constant　(K-m)　and　the　maximum　initial　rate　(V-max,),　we　deduced　the　reaction　mechanism　that　peroxynitrite,　catalyzed　by　mimic　enzymes,　directly　oxidized　tyrosine　combined　with　mimic　enzymes,　rather　than　decomposed　to　center　dot　OH　and　O-2(-).;　In　addition,　we　detected　the　rate　constant　of　the　reaction　catalyzed　by　these　two　kinds　of　enzymes　at　different　temperature　and　pH,　resulting　that　the　optimum　conditions　of　hemoglobin　to　catalyze　this　system　were　25　degrees　C　and　pH　8,　the　rate　constant　was　1.035　x　10(6)　mol(-1).s(-1),　while　hemin　was　37　degrees　C　and　pH　9.5,　the　rate　constant　was　6.842　x　10(5)　mol.L-1.s(-1);　Comparing　the　kinetic　parameters,　K-m　Hb　(4.46　mu　mol.L-1)　＜　K-m(Hemin)　(4.90　mu　mol.L-1),　V-max(Hb)　(0.072　Delta　I-F/s)　＞　V-max(Hemin)　(0.026　Delta　I-F/s),　we　discovered　that　the　rate　constant　of　hemoglobin　in　optimum　condition　was　greater　than　that　in　hemin,　and　the　catalytic　activity　of　hemoglobin　was　higher　than　that　of　hemin.　All　these　results　have　provided　kinetic　parameters　for　the　study　of　detatmiiiing　the　content　of　peroxynitrite　and　exploring　its　reaction　mechanism　with　enzymatic　method.　It　also　laid　a　theoretical　foundation　for　developing　new　diagnosis　technology　to　prevent　and　cure　diseases　caused　by　free　radicals　in　vivo.