Objective: To analyze the effect of the blood glucose gap on post-stroke cognitive impairment in acute ischemic stroke patients. Methods: 300 stroke patients admitted to the hospital between December 2021 and December 2022 were selected and divided into three groups according to the value of blood glucose gap: the group with no elevation of blood glucose gap (n = 124), the group with mild elevation of blood glucose gap (n = 97), and the group with elevated blood glucose gap (n = 79). The same treatment regimen was applied to these three groups and cognitive function was assessed using MMSE and MoCA at 3, 6, and 12 months after discharge. Results: The NIHSS and MoCA scores of the patients in the group with elevated blood glucose gap were significantly higher than those in the mildly elevated group and the non-elevated group at 3, 6, and 12 months after discharge, and the MMSE and MoCA scores of the patients in the group with mildly elevated blood glucose gap were significantly higher than those in the non-elevated group at 3, 6, and 12 months after discharge, and there were statistically significant differences between all the groups (P < 0.05). Conclusion: Patients with an elevated glycemic gap in acute ischemic stroke showed more pronounced cognitive impairment than those with no elevated glycemic deficit, and the severity of cognitive impairment increased with the degree of glycemic deficit.