Objective: To investigate the analgesic effect of dexmedetomidine combined ropivacaine on ultrasound guided thoracic paravertebral block in choledocholithotomy. Methods: Forty patients undergoing choledocholithotomy were selected with the age of 22–72 years, ASA grade I or II regardless of sex and divided into 2 groups by random number table (n=20): D group and C group. The right ultrasound guided thoracic 7 plane paravertebral nerve block and catheterization were performed in left supine position in both groups before anesthesia induction. D group was given 0.5% ropivacaine + 1 μg/kg dexmedetomidine 20 mL after postoperative awake and extubated. C group was given 0.5% ropivacaine 20 mL at the same time. The two groups were connected with intravenous self-controlled analgesia pump (sufentanil 1.0 μg/mL, dezocine 0.1 mg/mL, ondansetron 16 mg, 0.9% sodium chloride diluted to 100 mL) as a remedy for pain relief. Invasive blood pressure, ECG, respiration, pulse oxygen saturation after admission to the PACU were continuously monitored. Compared the difference of VAS and Ramsay scores of postoperative 2, 4, 8, 12 h between two groups, the use of additional analgesics and the incidence of adverse reactions. Results: After 2, 4, 8 h, VAS score in D group was significantly lower than that of group C, 4, 8, 12 h after operation in D group Ramsay score was significantly lower in group C (P<0.05). Compared to group C, the use of additional analgesics was less in group D (P<0.05). And the adverse reactions of two groups have no obvious difference (P>0.05). Conclusion: Dexmedetomidine combined with ropivacaine can promote the anaesthesia effect of ultrasound guided thoracic paravertebral block in choledocholithotomy.