Objectives To understand the anatomical relationship between the cervical sympathetic trunk (CST) and the cervical fascia and to provide a more reliable method for avoiding CST injury during the anterolateral cervical spine surgical approach. Methods Forty-two formalin-fixed adult cadaver specimens were divided into two groups. In the first group, the distance from the inner edge of the bilateral CSTs to the medial border of the longus colli muscle (LCM) and the distance between the CST and the midline of the cervical vertebrae were measured from the middle of the C3 vertebra through the C7 vertebra. The positional relationship between the CST and the superficial layer of the prevertebral fascia (alar fascia) was observed. In the second group, the carotid sheath and its contents were cut horizontally to observe the relationship between the CST and the carotid sheath. Results In the first group, the CST gradually converged medially and was closest to the medial border of the LCM at the level of the C7 vertebra. The distance from the CST to the vertebral midline was the smallest at the level of the C7 vertebra. In all specimens, the CST was closely adhered behind the alar fascia above the C7 vertebra and therefore could not be easily separated from the alar fascia by blunt dissection. In the second group, the CST in all specimens was tightly adhered behind the carotid sheath. Conclusion The CST was tightly adhered to the alar fascia and could be naturally retracted with the alar fascia. Retracting the alar fascia can effectively protect the CST.