Background A previous study indicated that gut microbiota changed notably in Graves' orbitopathy (GO) patients as compared to controls. However, the characteristics of intestinal bacteria in Graves' disease (GD) and GO are unclear. Objective The present study aimed to identify specific intestinal bacteria of GD and GO, respectively. Methods The gut microbial communities of the fecal samples of 30 GD patients without GO, 33 GO subjects, and 32 healthy subjects were analyzed and compared by 16S rRNA gene sequencing. Results At the phylum level, the proportion of Deinococcus-Thermus and Chloroflexi was decreased significantly in GO patients as compared to GD. At the genus level, the proportion of Subdoligranulum and Bilophila was increased while that of Blautia, Anaerostipes, Dorea, Butyricicoccus, Romboutsia, Fusicatenibacter, unidentified_ Lachnospiraceae, unidentified_Clostridiales, Collineslla, Intestinibacter, and Phascolarctobacterium was decreased in the GO group as compared to the GD group. Random forest analysis was used for the identification of specific intestinal microbiota, and Deinococcus-Thermus, Cyanobacteria and Chloroflexi were ranked in the top ten according to their contributions to sample classification. Moreover, compared to the control, there were multiple gut bacterial enrichment metabolic pathways in GO and GD patients, including nucleotide metabolism, enzyme family, and energy metabolism. Compared to GO, the only enrichment metabolic pathway found in GD was the viral protein family. Conclusions This study highlighted the significant differences in the intestinal microbiota and predictive functions of GD with GO, thereby providing new insights into the role of the gut bacteria that might contribute to the development of GO in GD patients.