The double flower developmental process is regulated via a complex transcriptional regulatory network. To understand this highly dynamic and complex developmental process of Dianthus spp., we performed a comparative analysis of floral morphology and transcriptome dynamics in simple flowers and double flowers. We found that the primordium of double flowers of 'X' was larger in size compared to that of simple flowers of 'L' in Dianthus chinensis. RNA-seq and Weighted Gene Co-expression Network Analysis (WGCNA) during flower development, identified stage-specific gene network modules. Expression analysis by RNA-seq indicated that a group of genes related to floral meristem identity, primordia position and polarity were highly expressed in double flowers genotypes compared to simple flowers genotypes, suggesting their roles in double-petal formation. A total of 21 DEGs related to petal number were identified between simple and double flowers. The experiments of in situ hybridization revealed that DcaAP2L, DcaLFY and DcaUFO genes were expressed in the intra-sepal boundary and petal boundary. We proposed a potential transcriptional regulatory network for simple and double flower development. This study provides novel insights into the molecular mechanism underlying double flower formation in Dianthus spp.