Objective:To evaluate the sedative effect of different doses of dexmedetomidine(Dex)combined with remifentanil(REM)under continuous epidural anesthesia(CEA)in total knee anthroplasty(TKA).Methods:125 patients who received TKA were included and divided into group A(n=42),group B(n=42)and group C(n=41)according to the different doses of Dex dur-ing anesthesia.On the basis of CEA,the three groups were intravenously pumped with 0.4,0.6 and 0.8 μg/kg of Dex respectively,and they were combined with 0.5 μg/kg of REM.The vital signs[mean arterial pressure(MAP),heart rate(HR)],sedation degree[bis-pectral index(BIS)]and stress response[plasma cortisol(Cor)]at the time of entering the room(T0),CEA puncture(T,),skin in-cision(T2),during 1 hour of surgery(T3)and at the end of surgery(T4)were compared between the groups,and the adverse reac-tions were observed.Results:The MAP at T1～T4 in the three groups was lower than that at T0(P＜0.05).Except for no statistically significant difference in HR between group B and group A at T4(P＞0.05),the MAP and HR of patients in all other time points were as follows:group C＜group B＜group A(P＜0.05).At T1～T4,the BIS values of each group were lower than those at T0.At T,,the BIS values of group B and group C were lower than those of group A(P＜0.05),but there was no statistically significant difference in BIS values between group B and group C(P＞0.05).At time T2～T4,the BIS values of group C were lower than those of group B and group A(P＜0.05).There was no statistically significant difference in BIS values between group B and group A(P＞0.05).At T2 and T4,the Cor values of all groups of patients were lower than T0.At T2,the Cor values of group C were lower than those of group B and group A.At T4,the Cor values of group B and group C were lower than those of group A(P＜0.05),there was no statistically sig-nificant difference in the Cor values between group B and group C(P＞0.05).The total incidence of adverse reactions in group C was higher than that in group B(P＜0.05),there was no statistically significant difference between group A and group B and C(P＞0.05).Conclusion:0.6 pg/kg Dex combined with REM under CEA has a good sedative effect on patients with TKA,and it can im-prove the hemodynamics and reduce the stress response,and has high safety.