OBJECTIVE：To investigate the effects of d exmedetomidine on postoperative delirium （POD） in liver tumor resection elderly patients with sleep disorder （SD）. METHODS ：Totally 80 patients undergoing liver tumor resection with preoperative Pittsburgh sleep quality index （PSQI）score ≥7 were selected from the Affiliated Cancer Hospital of Zhengzhou University from Jan. 1st，2020 to Oct. 31st，2020. They were randomly divided into group SD and group Dex according random number table ，with 40 cases in each group. At the same time ，40 patients with preoperative PSQI score ＜7 were selected as group C. Thirty min before anesthesia induction ，Dexmedetomidine hydrochloride injection 0.4 μg/kg was injected intravenously in group Dex. Etomidate emulsion injection ，Sufentanil citrate injection and Rocuronium bromide injection were used for anesthesia induction in 3 groups，and Ropofol medium/long chain fat emulsion injection + Remifentanil hydrochloride for injection was used to maintain anesthesia. The drug use ，operation time ，PACU stay time and postoperative hospital stay were recorded in 3 groups. The cognitive function was evaluated 2 h before operation and 1，3，5，7 days after operation. The occurrence of POD was observed. The plasma levels of IL- 6 and S 100β were measured 2 h before operation ，2 h after operation ，1，3，5 days after operation. The occurrence of ADR was recorded. RESULTS ：There was no statisti cal significance in intraoperativ e drug use and operation time among 3 groups （P＞0.05）. The PACU stay time ， the incidence of POD and the duration of POD in group SD an d lixxi18@126.com group Dex were significantly higher or longer than group C ， while the Dex group was significantly lower or shorter thangroup SD （P＜0.05）. The postoperative hospitalization stay ofgroup SD was significantly longer than group C and group Dex （P＜0.05），and there was no statistical significance between group Dex and group C （P＞0.05）. Before operation ，there was no statistical significance in MMSE scores or plasma levels of IL- 6 and S100β among 3 groups（P＞0.05）. MMSE scores of group C 1，3 days after operation ，those of group SD and group Dex 1，3，5 and 7 days after operation were significantly lower than those before operation. MMSE scores of group SD and group Dex 1，3，5 and 7 days after operation were significantly lower than group C at corresponding period ；the group Dex was significantly higher than the group SD at corresponding period （P＜0.05）. The plasma levels of IL- 6 and S 100 β at different time points were significantly higher than before operation ，and the group SD and group Dex were significantly higher than the group C ，and the group Dex was significantly lower than group SD at corresponding period （P＜0.05）. There was no statistical significance in the total incidence of ADR among 3 groups（P＞0.05）. CONCLUSIONS ：SD can promote the occurrence of POD in liver tumor resection elderly patients. Dexmetomidine can reduce the incidence of POD in elderly patients with preoperative SD ，the mechanism of which may be associated with the inhibition of IL- 6 and S 100β expression and the alleviation of brain injury with good safety.