Differentiated thyroid cancer includes papillary carcinoma and follicular carcinoma. 131I is an important tool for postoperative treatment of DTC. 131I treatment consists of two levels: first, 131I is used to remove residual thyroid tissue after DTC surgery, referred to as 131I nail clearance; second, 131I is used to remove metastases of DTC that cannot be removed by surgery, referred to as 131I nail clearance. 1. The significance of 131I nail clearing: (1) It facilitates the monitoring of disease progression by serum Tg and 131I systemic imaging. (2) The basis of 131I focal clearance treatment. (3) WBS and single photon emission computed tomography/CT fusion imaging after nail clearance are helpful for re-staging DTC. (4) Possible treatment of underlying DTC lesions. (2) Indications for nail clearing treatment: The indications for postoperative 131I nail clearing treatment are still controversial, and the main question focuses on whether low-risk patients benefit from it. Combining ATA’s recommendations, the actual situation in China and clinical experience, it is recommended that patients with postoperative DTC should be evaluated in real time and 131I nail clearing therapy should be selectively implemented according to TNM stage. Overall, 131I nail-clearing therapy can be considered except for all DTC with cancer foci <1 cm and no extra-glandular infiltration, lymph nodes and distant metastases. 131I nail clearing treatment is contraindicated during pregnancy, lactation, planned pregnancy in the short term and those who cannot follow the radiation protection instruction. 3.131I focal clearance treatment: For iodine-intake DTC metastases that cannot be removed surgically, 131I focal clearance treatment can be applied selectively. The first 131I focal clearance treatment should be performed at least 3 months after 131I nail clearance. After 6 months of focal clearance treatment, the efficacy can be evaluated. If the treatment is effective, focal clearance can be repeated with an interval of 4-8 months between focal clearance treatments. If serum Tg remains elevated after focal clearance treatment, or if imaging shows an increase in the size of the metastases, or if PET-CT reveals additional hypermetabolic lesions, this suggests that the treatment has no significant effect and termination of 131I treatment should be considered.