Branching is the main factor that determines plant architecture and is closely related to plant adaptation to the environment. Cold stress can inhibit lateral bud elongation in plants, but the underlying mechanism is still unclear. Here, we report that the cold stress-induced bZIP family transcription factor CmbZIP19 inhibits lateral bud elongation in chrysanthemum. We identified the target gene of CmbZIP19 as the brassinolide (BR) synthesis-related gene CmDWF1 by integrating RNA-seq and DAP-seq data. CmbZIP19 can directly bind to the ZDRE-like motif in the promoter region of CmDWF1, thereby inhibiting the expression of CmDWF1. We confirmed that CmDWF1 can promote the lateral branch elongation of chrysanthemum by genetic transformation. The branching phenotype of CmbZIP19-RNAi plants could be restituted by BR treatment. Taken together, the results suggest that CmbZIP19 modulates plant architecture by suppressing BR synthesis.