Objective To evaluate the treatment effect and influence factors of 131I therapy in patients with Graves hyperthyroidism. Methods A total of 792 patients (255 male, 537 female) with Graves’ hyperthyroidism were treated with 131I. 53 patients were pretreated with propylthiouracil (PTU), 428 patients with methimazole, and 311 received no antithyroid drugs. The serum FT4, FT3 and TSH levels in patients were measured and 131I uptake test, thyroid imaging were performed before the treatment. The thyroid function were measured after 1～3 months of 131I treatment. Results After 131I treatment among 792 patients, 221 patients (27.9%) were cured. 337 patients (42.6%) developed hypothyroidism, 140 patients (17.7%) improved, 44 patients (5.6%) relapsed, and 50 patients (6.3%) were ineffective. The total effective rate was 93.7% (742/792). There were statistical significance between the ineffective group and effective group in the levels of thyroid weight, the serum levels of FT3 and FT4, and the dose of 131I. The weight of thyroid, serum levels of FT3 and FT4 were most important factors in affecting 131I therapy. Conclusion 131I therapy for Graves’ disease is safe and effective. ATD may reduce the effectiveness of 131I treatment. The thyroid weight, serum levels of FT3 and FT4 are key influential factors for 131I treatment effect.