Primary objective: The 3-years disease-free survival was compared between low-dose group (30 mCi) and high-dose group (100 mCi). Secondary objective: The successful remnant ablation, efficacy, 3-year progression-free survival and safety were compared between low-dose group (30 mCi) and high-dose group (100 mCi). Research Hypothesis：The 3-year disease-free survival of low-dose group (30mci) may not be lower than that of high-dose group (100 mci) in intermediate-risk thyroid papillary carcinoma patients with no structural or functional lesions and stimulated thyroglobulin(ps-Tg)1-20ng/ml. Study design：Single-center, randomized, double-blinded Sample size：254 patients Follow-up：The measurement of serum thyroid function, thyroglobulin/ anti-thyroglobulin antibody(Tg/TgAb) and neck ultrasonography were performed every 3-12 months during the 3 years according to patients' condition, and computerized tomography(CT) scan, positron emission tomography/computed tomography(PET/CT) and diagnostic whole-body 131I scan were added if necessary. Intervention：Randomly allocated into two groups to receive either 30 mCi (low-dose group) or 100 mCi (high-dose group ) radioiodine for post-thyroidectomy ablation therapy. Evaluation index：Primary evaluation index: The 3-year disease-free survival. Secondary evaluation index: Successful remnant ablation, efficacy, the 3-year progression-free survival and safety.