Abstract: To construct a rapid, efficient method for assaying the fibrinolytic activity of nattokinase, two models between fibrinolytic activity of nattokinase in fibrin plate method and absorbance value of nattokinase in casein method or in TAME method were formed with the size of transparent zone as an intermediate parameter based on the study on fibrin plate method. The fibrinolytic activity can be directly determined by detecting the absorbance value of nattokinase in casein method or in TAME method.The results showed that the improved casein method can be applied in determining the fibrinolytic activity of nattokinase, the model in the improved method was as the following: y = 1877.77x-481.08 ( R2= 0.9924) .The result of verification experiment indicated that the model owned such advantages as strong correlation, high degree of accuracy, easy operation, high efficiency, and low cost.Therefore, the improved casein method was an efficient method for real time detecting the fibrinolytic activity of nattokinase.