This paper proposes using a precast diaphragm wall (PDW) for an urban low-carbon strategy. However, PDW using mechanized automatic construction still lacks the support of segmentation decision-making modeling. Therefore, this paper introduces the PDW LEGO®-inspired decision-making model (PDW-LDM) to address this problem. First, the paper establishes the parameterization, adaptive analysis, and decision-making modules. Second, it integrates these modules to create the PDW-LDM. Finally, the PDW-LDM is applied in a case study. The main conclusions include: (1) Multi-disturbance analysis revealed the most vulnerable disturbance case for PDW, indicating the need and feasibility of joints for PDW; (2) Legoized PDW exhibited both disturbance resilience and sufficient weight reduction (15%); and (3) A LEGO® frame model integrates with the hardware to build a complete set of equipment for PDW automatic construction. This paper provides a practical tool for decision-making in PDW automatic construction and promotes urban low-carbon strategy.