Sinojackia sarcocarpa, an endangered ornamental plant endemic to China, faces germination challenges that contribute to its endangered status. The mechanisms of its seed dormancy are not well understood. This study used morphological, physiological, transcriptomic, and gene function analyses to investigate these mechanisms. Our research shows that seed dormancy in Sinojackia sarcocarpa involves both physical and physiological factors. We found that removing the hard endocarp and applying gibberellic acid can effectively break dormancy. Transcriptomic analysis identified 2218 up-regulated and 374 down-regulated genes during germination. Notably, DOG1-domain genes SsDOGL4, SsTGA9, and SsTGA10 were significantly downregulated, while SsDOG1 was not. Additionally, overexpression of SsDOGL4 in Arabidopsis endosperm was found to enhance seed dormancy. Collectively, these findings offer significant insights into the mechanisms underlying seed dormancy in this endangered plant species.