Constructing open digital platforms is essential for industrial enterprises to achieve digital transformation and ecological synergy. However, systematic research on integrating external innovation capabilities with internal business systems through platform openness remains limited. This study employs a longitudinal case analysis of five pioneering industrial enterprises to elucidate the construction path and ecological synergy mechanisms of open digital platform capabilities. Findings reveal: (1) The construction of these capabilities follows a three-stage progression “open infrastructure—ecological synergy expansion—value co-creation iteration,” characterized by phases of “connection—symbiosis—evolution.” (2) “Digital-ecological” capabilities, facilitated by “introduction—collaboration—governance” strategies, achieve synergies across “technical interfaces—resource networks—rule systems,” transforming the platform from an instrumental infrastructure to an innovation ecosystem hub. This research reveals the dynamic laws of open digital platform capability construction, expands the intersection of open digital platform theory and ecosystem research, and provides actionable insights for industrial enterprises to accelerate ecological transformation through open strategies.