Objective To investigate the effect of saphenous nerve combined with posterior knee capsular block on cognitive function and analgesia after total knee arthroplasty (TKA).Methods A total of 96 patients with planned TKA who were admitted to our hospital from February 2018 to June 2021 were selected as the research objects, and divided into a control group, and a research group by random number table method, with 48 cases in each group. The control group was given saphenous nerve block, and the study group was given saphenous nerve combined with postcapsular block of the knee joint. The use of analgesic drugs and the recovery of the two groups during the perioperative period were counted, the postoperative pain conditions of the two groups were recorded, the postoperative cognitive function of the two groups was compared, and the inflammatory factors and knee joint range of motion were compared between the two groups before and after operation. The incidence of perioperative anesthesia-related adverse events in the two groups was counted.Results The dosage of remifentanil, the dosage of ketorolac tromethamine, the recovery time, the dosage of sufentanil during postoperative analgesia, and the ratio of PCA effective pressing times to total pressing times in the study group were all lower than those in the control group (P < 0.05). The visual analog scale (VAS) of pain at rest at 4 hours, 12 hours, 24 hours, and 48 hours after surgery was compared between the study group and the control group, and the VAS scores at different time points were different (P < 0.05). There was a difference in the VAS score between the group and the control group (P < 0.05). The VAS score of the study group was lower than that of the control group (P < 0.05), and the change trend of the VAS score between the study group and the control group was different (P < 0.05). The scores of the Mini Mental State Evaluation Scale (MMSE) were compared between the study group and the control group before operation, 24 hours after operation, and 48 hours after operation, there was no difference in MMSE scores between different time points (P > 0.05), there was no difference in MMSE scores between the study group and the control group (P > 0.05), there was no difference in the trend of MMSE scores between the study group and the control group (P > 0.05). Tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), β-amyloid (Aβ) before operation and 48 hours after operation in the study group was lower than that of the control group (P < 0.05). The range of motion of the knee joint of the affected limb was compared between the study group and the control group before surgery, 24 hours after surgery, 48 hours after surgery, and 72 hours after surgery, and there were differences in the range of motion of the knee joint between different time points (P < 0.05). There was a difference in the range of motion of the knee joint between the study group and the control group (P < 0.05), and the range of motion of the knee joint in the study group was higher than that in the control group (P < 0.05). There was a difference in the change trend of knee joint mobility between the study group and the control group (P < 0.05). There was no significant difference in the incidence of total adverse reactions related to anesthesia between the two groups (P > 0.05).Conclusion The saphenous nerve combined with retrocapsular knee block for TKA can reduce the consumption of perioperative analgesics, promote postoperative recovery, inhibit postoperative pain and inflammatory factors, and improve early postoperative knee range of motion with good safety.