Objective To investigate the influence of different doses of midazolam on early post-operative neurocognitive function for elderly patients with colorectal cancer and moderate and severe preoperative anxiety.Methods Eighty elderly patients undergoing elective colorectal cancer surgeries in Shunde Hospital of Southern Medical University, who were diagnosed as moderate and severe preoperative anxiety, were randomly divided into four groups (group C, group M₁, group M₂, group M₃), 20 patients in each group. And different groups represented different doses of midazolam at anesthesia induction. The induced dose of midazolam in group C, group M₁, group M₂, and group M₃ were 0 mg/kg, 0.05 mg/kg, 0.10 mg/kg and 0.15 mg/kg, respectively. The change of hemodynamic parameter, sedation-agitation scale, awakening time, extubation time, and pain score for four groups were observed and recorded. The MMSE and incidence rate of postoperative neurocognitive disorder in the four groups were recorded. The serum level of IL-1β, IL-6, and S-100β before induction of anesthesia, the first day after operation, and the seventh day after operation for all the patients were tested and recorded.Results There were statistical differences of MAP, HR in the four groups at different time (P < 0.05), but not among groups and trends (P > 0.05). The awakening time of group M₃ was significantly longer than that of the other three groups, and the extubation time of M₁ and M₂ groups were significantly shorter than that of the other two groups (P < 0.05). What's more, the VAS score and the incidence rate of agitation of group C was significantly higher than that of the other three groups (P < 0.05). There were statistical differences of MMSE for the four groups among different time, group and trend (P < 0.05). Based on the results of MMSE, the incidence of postoperative neurocognitive disorder in group C and M1 was significantly higher than that in group M₂ and M₃ on the first day after operation (P < 0.05). And at the seventh day after operation, 25% of the patients in group C still had postoperative neurocognitive disorder, which was significantly higher than that in the other three groups. There were no statistical differences the serum level of IL-1β (P > 0.05), but the serum levels of IL-6, S-100β were significantly different among different time, group and trend (P < 0.05).Conclusion Application of 0.10 mg/kg midazolam at anesthesia induction for elderly patients undergoing elective colorectal cancer surgeries, who were diagnosed as moderate and severe preoperative anxiety, was safe, reliable, with good recovery quality, less inflammatory reaction, and improved early neurocognitive function after operation.