ObjectiveTo explore the causes and surgical strategies of completion thyroidectomy for thyroid cancer. Method The clinical data of 35 patients with thyroid cancer who underwent completion thyroidectomy in Guizhou Provincial People’s Hospital from January 2020 to July 2022 were analyzed retrospectively. Results There were 23 females and 12 males, aged from 17 to 68 years (median 42 years). The nature of thyroid nodules in 22 patients was not determined at preoperative fine needle aspiration cytology or intraoperative frozen pathological examination, but the paraffin section examination after operation indicated thyroid cancer. Pathological examination after the first operation showed that 11 patients had a large number of lymph node metastasis in the central area (more than 5), and 2 patients were confirmed as medullary thyroid carcinoma. All the 35 patients underwent completion thyroidectomy at 5–93 days after the initial operation, among which 3 patients underwent resection of the affected side residual glandular lobe and isthmus ± ipsilateral CLN dissection, 18 patients underwent contralateral lobectomy and CLN cleaning, and 14 patients underwent contralateral lobectomy and lymph node dissection of the affected side cervical region (Ⅲ–Ⅳ region). The operative time was 45–135 min (median 105 min). Intraoperative blood loss was 10–50 mL (median 20 mL). One patient suffered from temporary recurrent laryngeal nerve injury after operation, and voice had returned to normal at 5 months after operation. Six patients showed temporary hypoparathyroidism, and serum parathyroid hormone returned to normal level in 1–3 months after symptomatic treatment. Nineteen patients were treated with iodine-131 after operation, and were followed-up for 1–16 months (median 12 months). No signs of tumor recurrence or metastasis were found. Conclusions Accurate preoperative and intraoperative evaluation of thyroid nodules and standardized surgery can reduce the incidence of completion thyroidectomy. For patients who really need completion thyroidectomy, adequate doctor-patient communication during the perioperative period, early response measures and appropriate completion thyroidectomy can reduce the probability of postoperative tumor recurrence and improve the survival of patients.