To explore the adjacent anatomic relationship and classification of Work Ⅰ congenital first branchial cleft anomaly（CFBCA） in order to guide clinical practice. The data of 48 cases of Work Ⅰ CFBCA with complete data were analyzed retrospectively. All 48 lesions were completely resected. 48 sides（100.0%） were anatomically preserved facial nerve, partial parotidectomy was performed on 33 sides（68.8%）, superficial lobe+deep lobe partial parotidectomy was performed on 9 sides（18.8%）, and 6 sides（12.5%） was not performed parotidectomy. External auditory canal reconstruction was performed on 32 sides（66.7%）; 43 sides（89.6%） underwent the anatomical preservation of the auricular lobe branch of the great auricular nerve; 9 sides（18.8%） was performed selective cervical lymphadenectomy at the same time. 45 sides of Work Ⅰ CFBCA presented irregular cystic or lobulated structure, the lesion was located below and behind the junction of the external auditory meatus bone and cartilage and distributed along the longitudinal axis of the external auditory canal; 3 sides were isolated in superficial lobe parenchyma of parotid gland. All lesions were located on the superficial surface of the main trunk and branches of the facial nerve. The average value of the shortest vertical distance between the lower edge of the lesion and the outlet of the main trunk of the facial nerve at the stylomastoid foramen was 7.2 （0-13.4 ）mm. Based on preoperative images and intraoperative findings, according to the adjacent relation with external auditory meatus , parotid gland and facial nerve, the classification of Work Ⅰ congenital first branchial cleft anomaly is proposed, which is specifically divided into 4 types: C1（posterior wall of the external auditory meatus） 17 cases（35.4%）, C2（inferior wall of the external auditory meatus） 13 cases（27.1%）, C3 （multi wall of the external auditory meatus） 15 cases（31.3%）, C4（isolated from parotid gland parenchyma） 3 cases（6.3%）. Work Ⅰ CFBCA has a close relationship with the adjacent anatomy of the region, and familiar with the classification of Work Ⅰ congenital first branchial cleft anomaly is helpful for the treatment of type and accurate resection.Copyright© by the Editorial Department of Journal of Clinical Otorhinolaryngology Head and Neck Surgery.