Abstract: Utilizing electricity consumption data from the Beijing-Tianjin-Hebei urban agglomeration, this study constructs a synergistic network for the transition from old to new growth drivers and delineates its spatial network structure. The research aims to explain the mechanisms through which the synergy network achieves enhanced connectivity, increased synergy intensity, and cross-regional diffusion. The analytical framework progresses sequentially from characterizing the phenomenon and interpreting the structure to identifying the underlying mechanisms. At the network level, the results indicate a continuous expansion of synergistic linkages during the sample period, with strong overall connectivity. However, network density remains relatively low, and structural concentration is high, suggesting that the formation and strengthening of synergistic ties rely heavily on a few key nodes. Structurally, analyses based on centrality and block models reveal a distinct role differentiation into core, hub, and peripheral cities, as well as a sectoral division characterized by the coexistence of net-spillover, net-beneficiary, and bidirectional-interaction blocks. Beijing and Tianjin play pivotal leading and spillover roles, while the hub functions of cities like Tangshan are strengthening. In contrast, participation from some peripheral cities remains limited, which explains the structural constraints on increasing network density. Mechanistically, Quadratic Assignment Procedure (QAP) regression results show that innovation proximity—measured by similarity in R&D investment—and geographical proximity significantly promote the formation and strengthening of synergistic ties. In contrast, isomorphism in the industrial structure of energy-intensive sectors exerts a suppressive effect. Based on these findings, this paper proposes an incentive mechanism for joint R&D and demonstration projects oriented toward cross-city co-production, a hub-city-based mechanism for outcome sharing and diffusion, and optimized rules for differentiated specialization and factor mobility in energy-intensive isomorphic sectors. These measures aim to enhance the quality of synergistic relationships and foster the coordinated development of regional structural transformation.