Objective To observe the effects of paravertebral block with different doses of dexmedetomidine combined with ropivacaine on emergence agitation of Pediatric thoracotomy.Methods A total of 120 children with thoracic surgery were randomly divided into four groups: dexmedetomidine groups (D1, D2, D3) and control group (group C).Groups D1～D3 were given with dexmedetomidine (0.5, 0.75, 1ug/kg)+0.375% ropivacaine, group C was given only 0.375% ropivacaine.The anesthesia duration , and postoperative recovery time (the end of operation to natural openning eyes), and the time of extubation were recorded. MAP and HR　were observed at the time point of the end of operation(T0 ),10 minutes (T1), 15 minutes (T2), extubation (T3) postoperation .Agitation scores was recorded at the time of extubation.Ramsay scores and adverse complications were recorded at the time point of 5 minutes (T4), 10 minutes (T5), awaking time (T6) after extubation.Results (1) Compared with group C ,the extubation time and recovery time were extended in group D1, D2 and D3 ,but there was no statistically significant difference .(2) MAP and HR of groups D1～D3 were significantly lower than group C at the time point of T0, T1, T2, T3 .MAP and HR of groups D2～D3 were significantly lower than group D1 at the time point of T0, T1, T2, T3 .There were no significant difference of MAP and HR between group D2 and group D3.(3)The Agitation scores in groupsD1, D2 and D3were significantly lower than that in group C at the time point of T3, and the Ramsay scores in groups D1, D2 and D3 were significantly higher than that in group C(P<0.05).The Agitation scores in groupsD2 and D3 were significantly lower than that in group D1, and the Ramsay scores in groups D2 and D3 were significantly higher than that in group D1(P<0.05).There was no statistically significant difference between group D2 and D3 .