Objective: To analyze the serological parameters of thyroid function and features of ultrasound examination in pediatric patients with Graves' disease (GD) and Hashimoto thyroiditis (HT) so as to provide evidence for the differential diagnosis of the two diseases. Methods: A total of 226 children (aged from 7-14 years) from January 2016 to December 2019 at Children's Hospital of Nanjing Medical University were enrolled, including 124 GD children (GD group) and 102 HD (HD group). HD children were further divided into HT with hyperthyroidism (HT with hyperthyroidism group, 38 cases) and HT with hypothyroidism (HT with hypothyroidism group, 64 cases). Two hundred healthy children with matching age were served as controls. Free triiodothyronine（FT₃）, free thyroxine（FT₄）, thyroid stimulating hormone (TSH）, anti-thyroid peroxidase autoantibody（anti-TPOAb）, anti-thyroglobulin antibody（anti-TGAb） and thyroid stimulating hormone receptor antibody（TRAb） were detected with electrochemiluminescence immunoassay（ECLIA）. Indices of ultrasonography including transverse diameter and anteroposterior diameter of right and left lobes of thyroid, isthmic anteroposterior diameter were measured, and blood flow in thyroid was detected by color Doppler flow imaging (CDFI). Both the thyroid function serological parameters and features of ultrasound examination were compared between the four groups. Results: Compared with HT with hyperthyroidism group, GD group had an increased TRAb level [(18.98±20.11） IU/mL vs. (0.33±0.41) IU/L] but lower levels of anti-TPOAb [(176.10±188.84) IU/mL vs. (219.65±203.66) IU/mL] and anti-TGAb[(242.40±632.15) IU/mL vs. (471.56±361.12) IU/mL]. A further analysis showed that the positive rate of TRAb in GD group was higher than that in HT with hyperthyroidism group, while HT with hyperthyroidism group had higher positive rates of anti-TPOAb（93% vs 52%） and anti-TGAb（84% vs 49%）. Percentage of GD group with rich blood flow detected by CDFI（94%） was higher than that of HT patients with hyperthyroidism group(35%）(P<0.05). Conclusions: GD pediatric patients have similar clinical features and size of thyroid with those of HT with hyperthyroidism, which make it difficult to differentiate. Patients with higher TRAb level and abundant blood flow by CDFI imply a high possibility of GD, while those with increased levels of anti-TPOAb, anti-TGAb and non-abundant blood flow by CDFI are likely to have HT with hyperthyroidism. CDFI may provide reference for distinguishing GD from HT with hyperthyroidism