With the advancement of building industrialization and sustainable development, modular demountable buildings, as an efficient and environmentally friendly form, show significant potential in scenarios such as emergency housing and rural construction. However, they face issues including insufficient component adaptability, low demounting efficiency, and low integration level. Based on the Design for Manufacturing and Assembly (DFMA) theory, this paper proposes solutions and takes M-Box1.0 as a case study to explore design strategies from four dimensions: product modularization, logistics optimization, rationality of demounting, and component integration. The results show that M-Box1.0 has excellent ventilation and lighting performance. Compared with similar products on the market, it has fewer parts and lower costs. Moreover, it reduces construction waste through prefabrication and demountable connections. This study clarifies the advantages of DFMA-oriented design and has practical significance for promoting the efficient and energy-saving development of building industrialization.