Street is believed as one of most important public spaces in a city, which carries the commuting, shopping, recreation, and communication functions of citizens’ daily life. However, during the rapid urban expansions, street spaces in cities have also encountered many troubles, such as decreased street space quality, diminished suitability for street-walking, insufficient street security, and low street vitality. Therefore, how to enhance the street walkability through human scale and how to build a healthy and sustainable city development model become core arguments in the relevant fields. Most of the previous research usually focuses on the transportation aspect of streets, addressing their accessibility and permeability, whereas the human-scale aspects of street space quality has been largely ignored. Therefore, this article selects street walkability as the research object, looking into a city’s central district area in specific. A multi-source database is established, based on urban 3D morphology big data, POIs data, and street image data for the quantitative analysis of this research. The results depict a fanshaped circular distribution pattern for the street walkability—measured into accessibility, convenience, comfort, and safety—in the central area of Nanjing city, consisting of a multi-core connected central area and scattered fringe areas. In addition, the interactive mechanism between street walkability and the influencers, such as urban 3D morphology, natural environment, landscape, and urban function distribution and POIs is found. Based on that, strategies with an aim of walkability optimization are further provided.