Abstract: Constructing open digital platforms has become a key pathway for industrial enterprises to achieve digital transformation and ecological synergy. However, there is still a lack of systematic research on how to integrate external innovation capabilities and internal business systems through platform openness. This study reveals the construction path and ecological synergy mechanism of open digital platform capabilities through a longitudinal case analysis of five industrial enterprises that were pioneers in building open digital platforms. The findings indicate that: (1) The construction of open digital platform capabilities follows a three-stage evolutionary path of “open infrastructure—ecological synergy expansion—value co-creation iteration,” characterized by the progressive features of “connection—symbiosis—evolution.” (2) The “digital-ecological” capabilities, through three major strategies of “introduction—collaboration—governance,” have achieved ecological synergy in “technical interfaces—resource networks—rule systems,” promoting the transformation of the platform from a tool-based infrastructure to an innovation ecosystem hub. The research results reveal the dynamic laws of open digital platform capability construction, expand the intersection of open digital platform theory and ecosystem research, and provide practical insights for industrial enterprises to accelerate ecological transformation through open strategies.