In open innovation projects (OIPs), project members from different participating organizations often have dual social identifications, namely, project identification and organizational identification. While such dual identifications may align or conflict in shaping collaborative behaviors, their micro-level psychological mechanisms and performance implications remain underexplored, as prior research predominantly adopts a firm-centric perspective. This study examines how dual social identifications affect OIP performance. The investigation considers mediating role of knowledge collaboration and the moderating role of resource interdependence. Data were collected through a questionnaire survey targeting the OIPs in major high-tech industrial development zones in China. The results show that project identification drives participating organizations to collaborate deeply (e.g., sharing core expertise) and broadly (e.g., involving diverse partners), both of which boost OIP performance. By contrast, organizational identification prioritizes expanding collaboration breadth over deep collaboration, which risks superficial engagement. Too many partners initially help but eventually harm OIP performance, whereas deeper collaboration consistently improves OIP performance. In addition, resource interdependence strengthens the positive effects of project identification on breadth and depth of knowledge collaboration but does little for organizational identification. This study extends social identity theory to the open innovation field and offers novel insights into practices of social psychological reality in OIPs, revealing how dual identifications interact with resource interdependence to shape OIP performance. Additionally, it offers actionable strategies for balancing knowledge collaboration breadth and depth while leveraging resource interdependence in OIP governance.