With the increasing efforts of the state to renew old settlements, the regeneration of existing houses built in the 1980s-2000s has entered a stage where it is urgent to transform from rough to refined transformation, but the diagnostic and assessment standards and decision-making basis for the pre-transformation stage have not yet been established. At the same time, the arrival of the era of informatization and intelligence also brings new opportunities and challenges for the diagnostic and assessment work of existing residential regeneration. Based on the existing research foundation of building regeneration, the article constructs a diagnostic and assessment process for the regeneration of existing residential buildings from an architectural perspective, which is divided into three phases: data collection and integration, visual model construction, and diagnostic assessment and analysis, and comprehensively applies the technology of building information modeling to carry out a comprehensive assessment using qualitative and quantitative diagnosis to form the template of diagnostic assessment. The diagnostic assessment template is formed, and an existing residence in Shenzhen is used as a case study object to apply the diagnostic assessment methodology and process, covering the collection of key element information, integration, diagnosis, and further assessment based on the diagnostic conclusions, to guide the design of remodeling programs. The study provides scientific guidance and decision-making direction for the practice of fine regeneration of existing residences and the formulation of related standard guidelines, improves the efficiency of decision-making, and has advanced demonstrative effect and foresight.