Ｏｂｊｅｃｔｉｖｅ　To evaluate the effect of dexmedetomidine (Dex) given by different routes on combined lumbar plexus and sciatic nerve block(CLPSNB) with 0.375% ropivacaine.　Methods　Ninety patients were randomly allocated into three groups (n=30): 0.375% ropivacaine 50 ml for CLPSNB in group R, 1 μg/kg Dex infused over 10 min+0.375% ropivacaine 50 ml for CLPSNB in group D+R, and 1 μg/kg Dex diluted in 0.375% ropivacaine 50 ml for CLPSNB in group DR. Groups R and DR were intravenously infused with the same volume of saline in group D+R. The onest time and duration of sensory and motor block, satisfaction of doctors, and side effects were recorded.　Results　Sensory and motor block onset time has no significant difference among three groups(P>0.05). Motor block duration and first time use of analgesics were longer in group DR[(768±246) min and (1 080±300) min] and group D+R[(732±204) min and (1 050±288) min] than group R[(420±126) min and (840±306) min](P＜0.05). Sensory block duration was longer in group DR[(1 008±258) min] than group D+R[(672±144) min](P＜0.05), while there was of no significance between groups R and D+R. The satisfaction of doctors was better in group DR(100%) than group R(85%)(P＜0.05). No complications occurred in all patients(P>0.05).　Conclusions　Dex diluted in 0.375% ropivacaine for CLPSNB can provide good analgesic efficacy and satisfaction of doctors.