Perform postoperative analgesia with femoral nerve anesthesia under the guidance of ultrasound for seventy patients undergoing anterior cruciate ligament reconstruction surgery, were into two groups: the control group R received 20 ml ropivacaine 0.2% (35 patients) Group D received 20ml ropivacaine 0.2% with 8mg/2ml dexamethasone intravenous (35 patients).