Many cities in China have undergone rapid urbanization and are experiencing a decline in residents' physical activity levels. Previous studies have reported inconsistent findings on the association between 3D's (density, diversity, design) and walking behavior, and few studies have been conducted in China. The aim of this study was to identify the association between objectively measured 3D's and different domains of walking (transport vs. leisure) in Hong Kong, China. A survey was conducted in 2014 to collect walking data and relevant individual data from 1078 participants aged 18–65. The participants were randomly selected from 36 Hong Kong housing estates with different built environment and neighborhood socioeconomic status (SES). Built environment factors—population design, land-use mix and street intersection density—were assessed using a geographic information system. Multi-level regression was used to explore the associations between walking behavior and built environment factors, while adjusting for covariates. Two out the three D's—land-use mix and street connectivity—are not significantly related to any domains of walking. Furthermore, the third D, population density, is only positively related to walking for transport and walking for leisure in the lower range of density, while is negatively related to walking for leisure in the higher range of density. The findings suggest that the association between original 3D's and walking may vary in different urban contexts. The policy or planning strategy—using three D's to promote physical activity—may be ineffective or even counterproductive in large and already dense cities in China.
