The use of urban space by vulnerable groups, especially ASD children with social anxiety, is an important part of building sustainable urban development. In this study, we focus on the play behavior of ASD children from the perspective of urban planning; then, we discussed how the urban built environmental factors affect the social behavior of ASD children. In this paper, 220 parents of ASD children were given questionnaires and 197 valid questionnaires were obtained after removing invalid ones. Stepwise regression was adopted to further accurately analyze the influence of each factor index in the built environment on children’s social behavior. The results showed that multiple urban built environment factors had significant influence on the social behaviors (observation, participation, retreat, and concealment) of children with autism at three stages: before departure, during journey, and arrived at destination. The purpose of study is to fully consider the use of urban space by ASD children when urban researchers or urban planners construct sustainable urban forms, formulate urban design guidelines, and implement old city renewal strategies.