Forsythia suspensa （Thunb.） Vahl is a perennial woody plant with dimorphic style and self-incompatibility. Mining the candidate genes for the development of heterostyly in Forsythia suspensa is of significance to reveal its evolution and development mechanism. The whole genome resequencing of 40 long style morph and short style morph Forsythia suspensa plants were conducted， followed by the SNP variation sites detection in the sample genome and the selection sweep analysis. The candidate regions （top 5% level） were screened by the combination of genetic differentiation coefficient Fst and the nucleotide polymorphism π ratio. Differentially expressed genes （DEGs） were analyzed by GO and KEGG enrichment annotation， and qRT-PCR was used to detect the transcriptional profiles of candidate genes at different periods of style development. Selective sweep analysis showed that 295 genes were under selection， which mainly played an important role in plant growth and development and metabolic regulation. By analyzing the pathways in plant hormone regulation， the candidate genes CYP734A1 （EVM0010386）， BRI1 （EVM0011829） and CYCD3 （EVM0018316） of heterostyly in Forsythia suspense were analyzed. The gene expression results indicated that the CYP734A1 gene has sustained high expression during the critical period of development in F. suspensa's S-morph flowers. The BRI1 and CYCD3 genes in the S-morph were significantly higher than those in the L-morph during the crown exposure period. The candidate genes excavated in this study were differentially expressed in the L-morph and S-morph style of F. suspensa. Brassinosteroids was involved in the development of the heterostyly in F. suspensa， which was one of the reasons for heterostyly of F. suspensa. Collectively， this study laid a foundation for the evolution and genetic development regulation mechanism of heterostyly in F. suspensa.