SiDWF1 encodes a gibberellin receptor GID1B-like protein controlling the internode length and plant height in sesame. Sesame is a high-height crop. Here we systematically analyzed the morphological and genetic characters of the sesame dwarf mutant dw607 (dwf1 type). The plant height and the internode length of dw607 significantly declined, while the thousand seed weight (TSW) significantly increased (P < 0.01). The cell size of stem parenchyma and pith tissue reduced, and vascular bundle cells and parenchyma tissue arranged much tighter in the dwarf mutant. Based on the cross-population association mapping of a RIL population of the cross 'dw607 (dwf1) × 15N41 (wt type),' the target interval linked to the short internode length was located on C9.scaffold2 of SiChr.4 in sesame. We further screened the 58 variants using the genomic variant data of 824 germplasm and BSA DNA pools and determined the target gene Sidwf1. The SNP mutation of C1057 to T1057 resulted in the amino acid change of P150 (proline) to S150 (serine) in SiDWF1. SiDWF1 gene allele is 1,638 bp and encodes a gibberellin receptor GID1B-like protein. Transcription profile assay reflected that Sidwf1 is highly expressed in leaf, stem, bud, and capsule tissues. The dynamic variation in endogenous GA3 content in dw607 and the wild type was also monitored in this study. The results revealed the molecular genetic mechanism of the internode length and plant height trait in sesame for the first time. The findings supply the theoretical and material basis for developing the marker-assisted selection (MAS) breeding in sesame.