Objective To study the optimum incision and reasonable extension of functional cervical dissection in well differentiated thyroid cancer. Methods The dissected specimens of 182 patients with well differentiated thyroid cancer treated by functional dissection(197 times), including therapeutic and selective dissection, from 1986 to 1998 were divided into 4 anatomical divisions(cervical inferior, media and superior area and subparotid gland area), and calculated the number of cervical lymph nodes that had been invaded by thyroid cancer in each area. Results The best incision was located in the area from the mastoid to downward and bakcward curvilinear to the surface and behind the anterior border of trapezium muscle 2～3?cm, then downward along the median of acromioclavicular joint to 5?cm below the midpoint of the clavicle. In therapeutic dissection group, among 61 patients with neck metastases, the metastases rate in the cervical superior area was 83.61%, but only one case in subparotid area. In selective dissection group, lymph nodes metastases was found in cervical superior area in 38.37% of patients, but none was found in subparotid gland ar ea. Conclusions The incision designed by authors is hard to see face to face. It is suitable for the young woman with thyroid cancer. There is almost no lymph nodes metastasis in the subparotid gland area, so it was unnecessary to dissect this area for it could reduce the operation time and extension of neck dissection. Able to protect the nerve function of spinal accessory, great auricular and lesser occipital nerve, so this operation can improve the life quality of patients with thyroid cancer.