The emission of carbon dioxide (CO) is a serious environmental issue, especially in Beijing-Tianjin-Hebei region. Unlike previous studies that mainly consider the bilateral and direct connection between two sectors, this study identifies path-based key sectors by considering the cascading effect of a sector on other sectors on paths of the entire economic system. We first construct an embodied CO emission flow network of Beijing-Tianjin-Hebei region, combining environmental input-output analysis and complex network theory. Then, the path-based key sectors are identified by traversing the path of each sector in the network based on cascading failure theory and hypothesis extraction method. On the one hand, the results show that a small number of sectors shoulder a large proportion of the embodied CO emission flows from both path and sector perspectives. On the other hand, we identify some path-based key sectors that did not receive enough attention from the sector perspective. Additionally, the sum of the embodied CO emission flows in about 30 steps accounts for 90% of the total embodied CO emission flows on its supply chain path. To more effectively reduce carbon emission, sectors that connect these 30 steps should be concerned in some policy recommendations. The method proposed in this paper can complement existing methods and contribute to further reducing CO emissions in the Beijing-Tianjin-Hebei region.