Brassinosteroids (BR) are class of important hormones in plants, which play a role in regulating plant growth and development and resisting various environmental stresses. BZR transcription factors are key regulatory factors in the BR signaling pathway and transmit BRs signals by regulating the expression of target genes. To further study the biological characteristics and functions of BZR genes in sorghum, this study identified 10 BZR genes from the sorghum genome, which were divided into four groups. The tissue-specific expression analysis showed that SbBZR3, SbBZR4, and SbBZR10 are highly expressed in multiple tissues as well as have high expression levels during the grain development process. Meanwhile, based on the resequencing results and grain phenotype data of 340 sorghum germplasm resources, the superior alleles of SbBZRs were identified. The results showed that the superior alleles SbBZR3-SNP458 (T) was significantly associated with grain length, and SbBZR10-SNP660 (A) was significantly associated with grain length, grain width and 1000-grain weight. Both SbBZR3-SNP458 (T) and SbBZR10-SNP660 (A) were artificially selected during the evolutionary process. This study not only lays a foundation for revealing the action mechanism of BZR genes in sorghum, but also provides a reference for using excellent alleles to improve grain size and promote the creation of new sorghum seeds with high yield.