To investigate the effect of tension on the contractive force of muscle and nerve conduction velocity of the repaired nerve, this study was designed. Fifty-four Sprague-Dawley (SD) rats were randomly divided into 3 groups. The left gastrocnemius muscles of the rats were dissected with the neurovascular pedicles intact; the tibial nerves were cut and immediately repaired by epineurial suture. Then the Achilles tendons were isolated and treated accordingly; the Achilles tendon was lengthened by 0.5 cm in lengthened group, shortened by 0.5 cm in shortened group and left alone in normal (control) group. In the 2nd, 4th and 8th weeks after operation, the isometric twitch contractive force of both the right and the left gastrocnemius muscles and the nerve conduction velocity (NCV) of the tibial nerve were measured. The shortened group showed greater isometric twitch contractive strength of the bilateral gastrocnemius muscles than those in the normal and lengthened groups in all the postoperative periods. The nerve conduction velocity (NCV) in the shortened group showed greater than other groups. A proper high tension of the muscle can increase the contraction of the muscle and may improve the nerve conduction velocity of the repaired nerve.