To investigate the stable TCM syndrome window in spontaneously hypertensive rats (SHR) associated with physical and chemical indexes and paves the way for further research on syndrome biological basis of hypertension. Method: We dynamically collected macro characterization, blood pressure, and behavioral tests of SHR and Wistar rats. NE and NO content in serum and brain were detected by Elisa and immunohistochemical method. Syndrome differentiation was conducted by equivalent transformation of animal characterization and clinical symptoms based on the clinical syndrome diagnostic criteria. Result: The 14 to 18 week-old SHR showed stable hyperactivity of liver fire syndrome. Compared to 10-12 week-old SHR and the same week-old wistar rats，14 to 18 week-old SHR serum and brain NE increased, while serum NO reduced(P<0.01). Conclusion: The stable time window of hyperactivity of liver fire syndrome in SHR is 14 to 18 weeks, associated with the increase of serum and brain NE and reduction of serum NO.