Aim. Postoperative delirium (PD) is a common complication of surgery in elderly patients, but its pathophysiological mechanism remains unclear. In order to clarify the role of intraoperative hypotension and fluctuation of blood pressure in the development of PD, we conducted a follow-up study in elderly patients with intraoperative hypotension and fluctuation of blood pressure. Methods. Patients who underwent hip surgery in 2018-2019 were selected. One day before the operation, the mentality of patients were evaluated by Mini-mental State Examination (MMSE), and the sex, age, height and weight of the patients were recorded. Radial artery puncture was performed in all patients before anesthesia, intraoperative SBP, MAP and DBP were recorded, and the surgical events of the patients was recorded. The markers associated with PD (TNF-α, IL-6 and S-100β ) were determined before and after surgery. Perioperative delirium（PD） was assessed by the prevailing standard of assessment, Confusion of Consciousness Assessment (CAM).. Cognitive assessment was evaluated using the Mini-mental State Examination (MMSE). In addition, the timing and type of delirium were recorded. Result. There were 158 patients which were accorded with the inclusion criteria came into the study. The results of our data showed that delirium occurred in 41 patients (25.9%) during the first week after surgery. In the comparison between the PD group and the non-PD group, it was found that the patients with postoperative delirium were older, lower body mass index and higher MMSE score before operation. Intraoperative blood pressure is low, usually more than 30% lower than preoperative blood pressure. The levels of TNF- α, IL-6 and Smur100 β were higher after operation. Conclusion. The increased incidence of postoperative delirium may be related to intraoperative hypotension and intraoperative blood pressure fluctuation. The pathophysiological mechanism may be that hypotension causes low cerebral perfusion, which in turn causes local inflammation in the brain. In addition, postoperative delirium is also more likely to occur in older patients with lower body mass index.