Objective To evaluate analgesic effect of dexmedetomidine (DEX) combined with ropivacaine in single sciatic nerve block after total knee arthroplasty (TKA) with continuous femoral never block.Meth ods One hundred and twenty patients,ASA physical status Ⅰ ～ Ⅱ,who underwent unilateral TKA were randomly allocated into two groups:group D (DEX with ropivacaine);group R (ropivacaine only).Both groups experienced spinal-epidural anesthesia.Continuous femoral nerve block was performed after operation.Rest and movement visual analogue score (VAS),Ramsay sedation scores were recorded.In addition to the date of the analgesia drug dose,the pressed times of PCA,the mobility of knee joint and the force of quadriceps femoris were obtained at different points of time.Results Rest Pain scores (RVAS) of the group D were lower at time point 8,12,24,36,48 h and Ramsay sedation scores were higher at time point 4,8,12 h than that in the group R (P ＜ 0.05).The analgesia drug dose and the pressed times of PCA reduced in the group D.The range of motion (ROM) was better in the group D at 1 d,2 d after operation (P ＜ 0.05).There was no significant difference in the force of quadriceps femoris in both groups.Conclusion Dexmedetomidine combined with ropivacaine in single sciatic nerve block after TKA provided better analgesia when continuous femoral nerve block was performed.Meanwhile,analgesia lasted longer and did not increase the motor nerve blockade.