Objective To observe the postoperative use of dexmedetomidine as a sedative and analgesic agent in pediatric patients undergoing cardiac surgery. Methods Forty pediatric patients undergoing atrial septum defect repair or ventricular septal defect repair surgery , aged 1 ~ 7 years old, with body weight 8 ~ 25 kg and ASA Ⅰ ~ Ⅱ level, were enrolled, and randomly divided into two groups, the experimental group and the control group, 20 cases in each. The patients assigned to experimental group received a continuous infusion of dexmedetomidine, dose of 0.3 ug.kg-1.h-1, starting at the beginning of seam the skin and continuing for 24 hours postoperation, and isodose normal sodium as placebo was infused to the control group patients. The FLACC scores and the Ramsay scores were graded by a unaware nurse at 4，8，12，16，24 hours postoperation. Once the FLACC scores higher than 6 were graded or the Ramsay scores reach 1, midazolam 0.1 mg/kg was injected intravenous. The MAP and HR were recorded at the corresponding time points. Side effects were assessed during the first 24 hours. Results Compared with the control group，the FLACC scores were lower and the Ramsay scores were higher at the 8, 12, 16, 24 hours postoperation in the experimental group, and the times and doses of medazolan use throughout 24 hours were lower respectively（p<0.05）. No postoperative respiratory depression and bradycardia was identified. Conclusion Continuous infusion of dexmedetomidine with a dose of 0.3 ug.kg-1.h-1 may be associated with increased postoperative pain relief and sedation in pediatric patients undergoing cardiac surgery.