【Abstract】 Objective To investigate effects of dexmedetomidine on sedation, respiratory depression and hemodynamics in elderly patients underwent combined spinal epidural anesthesia. Methods 91 elderly patients underwent combined spinal epidural anesthesia in our hospital from May 2017 to May 2018 were enrolled and divided into group D (dexmedetomidine) and group M (midazolam) according to the different sedative medications. The alertness / sedation (OAA/S) scores, heart rate (HR) and mean arterial pressure (MAP), respiration rate (RR) and oxygen saturation (SpO2) were recorded at five time points, e.g. before anesthesia (T0), 10min (T1), 20min (T2), 30min (T3) and 60min (T4) after sedative administration were observed. The adverse reactions were also recorded. Results The OAA/S scores at T1~T4 were decreased in both groups compared with those at T0, and were lower in group M than in group D (P＜0.05). The HR of two groups at T0~T4 had no difference (P＞0.05); The HR in the group M at T1~T4 had no difference with that at T0 (P＞0.05), while in group D, the HR at T1~T4 was lower than that at T0 (P＜0.05). The MAP level of group M at T2~T4 was lower than that of group D (P＜0.05). The MAP levelat T1~T4 were lower than those at T0 in both groups(P＜0.05). The SPO2 at T1~T4 in group M was lower than that of group D (P＜0.05). The SPO2 in the both groups at T1~T4 had no difference with that at T0 (P＞0.05). The incidence of adverse reactions including body motion, nausea and vomiting, respiratory depression, upper airway obstruction, and chills in group M was 378%, which was higher than 87% in group D including body motion, upper airway obstruction, and chills. Conclusion The application of dexmedetomidine exists good sedative effect, mild respiratory inhibition and stable hemodynamics for elderly patients underwent combined spinal epidural anesthesia, which can reduce the incidence of adverse reactions such as chills, nausea and vomiting, body movement and airway obstruction.