Promoting physical activity is an effective way to improve healthy level of older adults under the background of “healthy aging”. The related research of physical activity is important, and has become a hotspot between multiple disciplines at home and abroad. Thus, based on the perspective of health, this study mainly focused on walking that is very common and is beneficial to older adults’ health in daily life, and examined the influence of built environment on walking by using survey data of physical activity in Nanjing, and eventually provided useful exploration for relevant theories and practices. The results show that: (1) The range of daily walking space can be used as the basis for identifying the built environment boundary involved in walking, and the main places can be used to identify the differences in the demand of built environment elements. Specifically, a place within 1000 meters from home is the major walking space for older adults, and that within 2000 meters is also an important option. Moreover, there are significant differences in the choice and use of major destinations among older adults among different space distances. (2) The density of public open space, commercial and public service facilities involved in daily life, and the subjective perception of built environment have a significant impact on the transportation/leisure walking of older adults. The intensity of commercial and public service facilities, public space, traffic facilities, the perception of road intersection density, safety and flatness have positive or negative influences on participation or amount of transportation walking. The intensity of public space, residential density and the perception of accessibility of public space, road night lighting and flatness have positive or negative impacts on participation or amount of recreational walking. In addition, with the extension of the range of active space, the influence of subjective and objective spatial characteristics is weakened or strengthened. (3) According to the daily walking habits of older adults and the influence of urban built environment on walking, this study attempts to propose planning strategies from the aspects of providing walking space involved in daily life and promoting a healthy lifestyle.