Objective To investigate ultrasound guidended nerve block of femoral nerve in emergency operation.Methods 40 patients who planned to accept surgery of feet,lower limb under knee.They were randomly devided into 2 groups:ultrasound guidended group and the control group.Femoral nerve and Sciatic nerve were blocked by ultrasound guidended technique or classic landmark technique.1.5% lidocaine was administered for nerve block.Sensory block was observed every 5 minutes in 30 minutes.Onset time,effect of anesthesia,algesia time and complications were recorded.T-test and varience difference were applied.Results The onset time of local anesthetics was faster in the ultrasound guided group than that of the control group.Effect of analgesia was better in in the ultrasound guided group than that of the control group. Conclusion Nerve block of femoral nerve and the sciatic nerve guided by ultrasound was better than the classic technique.