Sustainable urban forms (SUF) guide spatial creation, significantly revitalise the development of traditional settlements, and are an essential theoretical support for urban design. At the same time, the emergence of quantitative spatial analysis technology further promotes the visualised evaluation of the performance of spatial vitality in urban design. However, current research rarely studies the spatial vitality of traditional settlements with quantitative spatial analysis from the SUF perspective. Therefore, this research takes Anren Ancient Town in Chengdu, Western China, as an example to propose a design based on sustainable urban form theory to raise local spatial vitality. Then, it introduces the vitality evaluation system based on the urban form index (UFI) with three measurement methods: Space Syntax, Spacemate, and MXI, and conducts a comparative spatial vitality evaluation of Anren Ancient Town’s status quo to explain the process of how the design scheme came about. The results found that urban design proposals based on the principles of compactness, mixed land use and diversity in SUF design guidelines can effectively improve the vitality of traditional settlements. The high vitality of an urban settlement could be achieved by combining SUF-based design guidelines and UFI-based evaluation systems. The spatial vitality evaluation system based on the SUF could assist and optimise decision-making in design and act as a paradigm for urban design or urban regeneration in traditional towns.