In the context of increasingly extreme high temperatures during the summer in cold regions, the spatial vitality of urban blocks is significantly affected. In order to enhance the summer vitality of sustainable urban neighborhoods, this study explores the mechanisms of street elements and vitality under the guidance of thermal comfort. Taking an urban pedestrian street in Sanlitun, Beijing, during a summer day as the research subject, this study systematically analyzed the impact of environmental factors such as street orientation, aspect ratio, three-dimensional greenery of trees, and tree spacing on the thermal comfort of street space. By quantitatively analyzing the relationship between thermal comfort and pedestrian vitality in different street spaces, this study reveals the mechanisms by which environmental factors enhance the summer usability and spatial vitality of pedestrian streets. The research results indicate that street vitality shows a gradually increasing trend throughout the day, particularly between 12:00 and 16:00, when thermal comfort significantly affects people’s vitality. Furthermore, univariate analysis reveals that the street aspect ratio is the primary factor influencing the spatial vitality of the southern section of the Sanlitun Taikoo Li pedestrian street, with a characteristic average of 8.28 over a week. Finally, the results of the multi-factor analysis show that, when enhancing street vitality, priority should be given to the interactions between street aspect ratio, tree greenery, temperature, and physiological equivalent temperature, where the correlation coefficient between street aspect ratio and vitality is 0.70, and that between temperature and physiological equivalent temperature is 0.63, both showing positive correlations. Research shows that, in street planning, a reasonable building aspect ratio (1:2 to 1:4) and scientific green design are key. By carefully controlling the planting density and greenery configuration of trees, optimal street space effects can be achieved. This study proposes sustainable urban design strategies by optimizing street space design and improving environmental thermal comfort, aiming to enhance the summer vitality of urban blocks in cold regions and advocate for a sustainable development model that combines ecological and social benefits.

With the acceleration of urbanization, existing studies have primarily focused on the influence of either built environment factors or thermal comfort on street vitality, while their synergistic effects remain underexplored. This study selects four pedestrian commercial streets in Beijing and Chengdu for dual validation to reveal the varying impacts of built environment elements on street vitality under different climatic conditions and to uncover the diurnal dynamic effects. The key findings include the following: (1) the shop width (optimal between 8 and 14 m) and the number of items of street furniture are the core drivers of vitality across time and space; (2) although the visibility of greenery is often recommended to boost vitality, its influence is nonlinear and closely tied to thermal comfort; (3) thermal comfort and street width dynamically affect the spatiotemporal variations in vitality; and (4) daytime vitality is mainly driven by spatial comfort related to commercial density, furniture, and thermal comfort, while nighttime vitality relies more on the synergy between street width and shop transparency. This study aims to support differentiated street design across climates, enhancing both economic vitality and sustainable urban development.