Abstract: Engineering machinery products have typical characteristics of "single piece small batch, complex process, and strong customization personality". Traditional rigid production lines expose systematic difficulties such as layout solidification, long switching time, and logistics redundancy when responding to mixed production of multiple varieties. On the basis of defining the connotation characteristics of flexible digital production lines, this article constructs a dynamic model of equipment layout that integrates logistics entropy constraints, proposes a "planning simulation feedback" closed-loop iterative layout planning method based on digital twins, and establishes a multi-level efficiency improvement mechanism for flexible production lines. Research has shown that the layout optimization of flexible digital production lines is essentially a process of mapping enterprise level flexible strategies layer by layer into manufacturing system structural parameters, and the breakthrough point for efficiency improvement lies in grasping the core mediating variable of "dynamic response capability". The research results provide theoretical basis and methodological support for the digital production line transformation of construction machinery enterprises。