Abstract: Objective To investigate the effects of dexmedetomidine on desflurane-mediated sympathoexcitation.Method Sixty patients undergoing elective thoracic surgery at Xuzhou Medical University Hospital were randomly divided into two groups: desflurane group (group C) and dexmedetomidine combined with desflurane group (group D). patients in group C were treated with 0.1 ml/kg of normal saline within 10 minutes before induction of anesthesia, then the dose was changed to 0.05 ml/( kg·h) of physiological saline. patients in group D were treated with 0.5 μg/kg dexmedetomidine within 10 minutes before induction of anesthesia, then the dose was changed to 0.5 μg/(kg·h) of dexmedetomidine. MAP、HR、L/H and plasma norepinephrine(NE) , epinephrine(E) were recorded after entering the operating room(T 0)and 1min，2min，3min，4min，5min （T1、T2、T3、T4、T5）after the concentration of desflurane reaching 1.0 minimum alveolar anesthetic concentration (MAC).Result The MAP, HR, LF/HF, E and NE in blood in Group C from T 1 to T 5 were higher than those of the T 0 time point( P<0.05). The MAP, HR, LF/HF, E and NE in blood in Group D from T1 to T 5 were higher than those of the T 0 time point, and the difference was not statistically significant ( P>0.05); the findings of comparing the two groups: the difference of MAP, HR, LF/HF, E and NE in blood at T0 time point was not statistically significant ( P>0.05), and the difference was statistically significant at T3 and T4 ( P<0.05). The difference of HR, LF/HF, E and NE in blood at T5 was statistically significant ( P<0.05). Conclusion Dexmedetomidine can inhibit desflurane-mediated sympathetic excitation ,which is beneficial for maintaining perioperative hemodynamic stability and reducing perioperative complications.