The coordinated management of full-lifecycle investment plans in the infrastructure sector is a key factor in ensuring the high-quality development of infrastructure. Currently, infrastructure projects face numerous challenges in full-lifecycle management, including gaps between phases, a lack of multi-stakeholder collaboration, and errors in plan execution, which severely hinder overall improvements in investment efficiency. Building upon these issues, this paper conducts research from the dual perspectives of mechanism establishment and efficiency enhancement. On the one hand, it establishes a comprehensive collaborative management mechanism system by addressing aspects such as the design of an integrated full-cycle framework, multi-tiered collaborative organisational structures, the development of digital platforms, and collaborative risk response. On the other hand, it explores effective mechanisms for improving efficiency through standardised process re-engineering, dynamic monitoring and feedback, precise resource allocation, and institutional and talent safeguards, thereby providing a reference for improving the overall level of collaborative management of investment plans in the infrastructure sector.