Objective: We are going to study the influence of persistent infusion of dexmedetomidine on pediatric postoperative emergence agitation. Methods：72 ASA I~II`patients aged 4-10 years old , scheduled for fractures open reduction and internal fixation surgery under general anesthesia were randomly allocated to four groups. Patients in group PD received propofol and dexmedetomidine（0.5μg·kg-1·h-1）,while patients in group PN received propofol and sodium chloride. Patients in group SD received sevoflurane and dexmedetomidine, while patients in group SN received sevoflurane and sodium chloride. HR、MAP、BIS were recorded before drug delivery (T1 ),10 minutes (T2 )、20 minutes （T3）、30 minutes（T4） after administration and after extubation（T5）. Time from stopping narcotic drugs to extubation (T6 ) and opening eyes(T7 ) were determinated. The score of postoperative degree of agitation and pain was measured. The incidence rate of agitation in recovery period was also caculated. (agitation score greater than 3). Results:(1) The extubation time (7.1±2.6vs4.4±2.1min、7.3±2.1vs4.9±2.0min)and opening eyes time (16.3±5.7vs9.8±3.1min、13.4±5.8vs8.8±5.0min)were both prolonged significantly when group PD compared with group PN and group SD compared with group SN（P<0.05）.There is little statistical difference between group PD and group SD（P>0.05）.(2) The postoperative agitation score (1vs2、3vs4) and pain score (CHIPPS, 2.5vs3、4vs7) were also decreased in group PD and group SD compared with group PN and group SD respectively（P<0.01）.The incidence rate of postoperative agitation was decreased significantly in group SD (group SD 5.6%VS group SN 33.3%)（P<0.05）. The emergence agitation score of group PD was lower than of group SD（P<0.05）. Conclusions:Although dexmedetomidine may prolong the palinesthesia, it can decrease the postoperative agitation score and the pain score. The postoperative agition incidence rate is also reduced significantly. The patients may feel more comfortable.