Objective To study the anatomic relationship of the thoracic phrenic nerve and provide anatomic basis for harvesting whole length phrenic nerve under direct vision using thoracoscope in the treatment of brachial plexus root injuries. Methods The anatomy of thoracic phrenic nerve and its surrounding tissues were observed on 20 sides of 10 adult cadavers which were embalmed by 10% formalin. Video-assisted thoracoscopic transthoracic phrenic nerve harvesting was carried out in the surgical treatment of 17 cases of brachial plexus injuries. The results in these cases were summarized. Results If the cutting end of phrenic nerve was pulled out of the second intercostal space at the anterior axillary line,the ratio of its location in the upper arm was (38.60±13.10)% on the left side and (52.40±7.90)% on the right side. If the cutting end was pulled out of the thoracic outlet,the location ratio in the upper arm was (25.90±11.50)% on the left side and (39.00±6.90)% on the right side. The ratio of phrenic nerve between d (length from medial edge of the incision to the pleural top) and f (length from pleural top to the top of diaphragm) was (0.84±0.23) on the left and (0.96±0.15) on the right at third intercostal space,(1.02±0.21) on the left and (1.08±0.17) on the right at the fourth intercostals space. The ratio of phrenic nerve between e (length from medial edge of the incision to the insertion of diaphragm) and f (length from pleural top to the top of diaphragm) was (0.66±0.15) on the left and (0.60±0.21) on the right at third intercostal space,(0.55±0.04) on the left and (0.44±0.05) on the right at the fourth intercostals space. Endoscopic-assisted transthoracic phrenic nerve harvesting in 17 cases of brachial plexus root injuries obtained full length of the phrenic nerve that could be directly coapted to the muscle branch of the musculocutaneous nerve. No complications were noted.The strength of the biceps underwent good recovery,which was M2 to M4. Conclusion The phrenic nerve in the thoracic cavity is suitable for full-length dissection based on the anatomical characteristics. Endoscope-assisted transthoracic phrenic nerve harvesting is a simple and safe surgery with low requirement of special equipment,and can be carried out as a routine surgery.