Despite the importance of motivation in driving the formation of collaborative risk management, the existing literature lacks recognition of stakeholders’ motivations to participate in the collaborative risk management of mega infrastructure projects. By combining interview data with the theoretical framework based on previous literature, this study constructs a motivation framework for stakeholders to participate in collaborative risk management of mega infrastructure projects, comprising four groups of motivations formed by glue identity logic (organizational or individual level) and interest logic (intrinsic drive or extrinsic stimulus). Motivational differences between project owners and contractors are discussed based on the case study of the Hong Kong-Zhuhai-Macao Bridge, indicating that these differences are closely related to the identity of stakeholders and project progress. This study contributes a systematic perspective to recognize the motivations behind participation in collaborative risk management of mega infrastructure projects, aligns managerial intentions with actual motivations, and uncovers new insights into collaborative risk management. It enriches the collaborative risk management theory in mega infrastructure projects and provides guidance and inspiration for practitioners in decision-making and collaborative risk management in such projects.