To investigate the effect of preemptive femoral nerve-sciatic nerve block on postoperative short-term cognitive function and analgesia in patients with tibiofibula fracture.Methods The patients were randomly divided into control group (postoperative block group,n=70) and observation group (preemptive block group,n=70),patients in both groups were treated with general anesthesia combined with femoral nerve-sciatic nerve block. Postoperative short-term cognitive function ［mini-mental state examination(MMSE) and delirium scale(CAM) were assessed respectively and jointly］in the two groups at different time points［1day(T0),3days(T1),5days(T2),7days(T3)after operation and the day of discharge (T4)］were analyzed. The analgesic effects［the pain score at rest and activity measured by visual analogue scale (VAS) at T0,T1,T2and T3,the postoperative remedial analgesia rate, the duration of nerve block, the total amount of remifentanil］ were analyzed. The total amount of propofol, postoperative recovery time, length of stay, the rate of complications and continuing rehabilitation treatment were compared between two groups.Results There was no significant difference in the rate of postoperative cognitive dysfunction and postoperative delirium between the two groups at different time points(T0,T1,T2,T3 and T4).When the two scales were used to evaluate short-term cognitive function, at T0,the rate of perioperative neurocognitive disorderswas significantly decreased in observation group as compared with control group (12.90% vs 26.98%, P=0.049), but there was no significant difference in the rate of perioperative neurocognitive disorders between the two groups at T1,T2,T3 and T4.At T0,the pain degree at rest and activity in observation group was significantly lower than that in control group (P＜0.05). In addition, the duration of nerve block in observation group was longer as compared with control group (20.55±6.22 vs 16.47±6.59, P=0.001),the total amount of remifentanil in observation group was lower than that in control group (1001.51±798.79 vs1374.29±783.13, P=0.002).The postoperative recovery of observation group was significantly faster as compared with control group (7.00±2.40 vs12.37±3.59, P＜0.0001).Conclusion The operation of tibiofibula fracture and the advance application of femoral nerve-sciatic nerve block are more beneficial to the short-term cognitive function and perioperative analgesia, and the recovery is accelerated