Abstract: Objective To investigate the effect of ultrasound-guided thoracic paravertebral block with dexmedetomidine and ropivacaine on postoperative analgesia in open liver surgery. Methods Total 40 patients with ASA Ⅰ to Ⅱ in our hospital between January, 2016 and January, 2017 were randomly divided into two groups. In group D, 0.5% ropivacaine 20 ml with 1 μg/kg dexmedetomidine were injected into thoracic paravertebral space guided by ultrasound. In group C, 0.5% ropivacaine were injected into thoracic paravertebral space. The mean arterial pressure (MAP) and heart rate were recorded before the induction of general anesthesia, immediate after the tracheal intubation, the beginning of the operation, 30 minutes after the operation and the end of the operation. The visual analogue scale (VAS) of pain at rest and physical activity state and the Ramsay scores were recorded immediate after extubation, 4 h after operation, 12 h after operation, 24 h after operation, and 48 h after operation. The effective pressing numbers and the adverse reactions were recorded. Results Immediate after the extubation, the Ramsay scores of group D was significantly higher than that in the group C; there was no significant difference in the VAS of pain at rest or physical activity state between the two groups. Four, twelve and twenty-four hours after the operation, the Ramsay scores of group D was significantly higher than those in the group C, and the VAS of pain at rest and physical activity state was significantly lower than that in the group C. There was no significant difference in MAP and HR between the two groups at every time of anesthesia; there were no nausea and vomiting, respiratory depression and other adverse reactions in the two groups. Conclusion 0.5% ropivacaine 20 ml with 1 μg/kg dexmedetomidine can safely enhance the effect of thoracic paravertebral nerve block (TPVB) and prolong the duration of analgesia in open liver surgery.