To assess the effects of length of continuous femoral catheter on blockade of femoral nerve, lateral femoral cutaneous nerve and obturator nerve.In the study, 70 patients with American Association of Anesthesiologist grades I-II undergoing total knee arthroplasty were randomly divided into three groups, femoral nerve catheters were inserted 5 cm, 10 cm or 20 cm with assistance of a nerve stimulator, patient-controlled analgesia pumps were connected after load of 30 mL 0.3% ropivacaine via the catheters. Sensory blockade of the femoral nerve, lateral femoral cutaneous nerve and obturator nerve were recorded at 24 h postoperatively. Visual analog scale (VAS) pain scores during rest and motion were recorded at 24 h and 48 h postoperatively.The blockade effect of lateral femoral nerve in the 20 cm group was the best. There was no significant difference in sensory blockade between the 5 cm group and the 10 cm group. There was no significant difference in VAS score among the three groups.When continuous femoral nerve block is used for postoperative analgesia after total knee arthroplasty surgery, the catheters that are inserted 5 cm, 10 cm or 20 cm could provide similar and satisfying analgesia effect.