Objective To explore the efficacy and safety of seaweed-laminaria combined with methimazole in the treatment of primary Graves’ disease. Methods 42 patients with Graves’ disease were randomly divided into two groups. The experimental group was treated with seaweed-laminaria combined with 2/3 conventional dose of methimazole, while the control group was only given conventional dose of methimazole. After 4 weeks,the thyroid function (FT3, FT4, TSH), Graves’disease-specific autoantibodies(TRAb), thyroid size(ultrasound evaluation), TCM syndrome score, use Flow cytometry to identify PD-1 and PD-L1 on CD4+ CD25+ Treg and adverse reactions in the two groups were observed. Results After treatment, compared with before treatment, the total effective rate after excluding discontinuation of the drug due to adverse reactions and the regimen changing was 100%. Thyroid function, TCM syndrome score and TRAb were significantly decreased(P＜0.05); the thyroid function, TCM syndrome score, TRAb decline degree and thyroid shrinkage degree of the experimental group were significantly better than those of the control group(P＜0.05). CD4+ CD25+ Treg、PD-1+ Treg、PD-L1+ Treg、PD-1+ /PD-L1+ Treg degree of the experimental group were significantly better than those before treatment（P＜0.05）. Conclusion Seaweed-laminaria combined with methimazole in the treatment of newly diagnosed Graves’ disease could quickly control thyroid function,improve symptoms,and regulate immune function.