[Objective]The influence of Hirulog-s in mutual activation reaction system constituted by single chain urokinase-type plasmi nogen activator (pro-uPA) and plasminogen(plg) were studied in this paper.[Methods]The Enzymatic reaction kinetic constant (Km,kcat) of plasmin(plm) acts on pro-u1PA in mutual activation reaction system influenced by pro-uPA and pig was measured.And the impact of Hirulog-s on the catalytic reaction activity and affinity by comparing kinetic constants of the enzymatic reaction in different concentrations of Hirulog-s was investigated as well.The role of fibrinolytic activity was detected by enzyme substrate reaction.