The rapid urbanization process in China has led to a significant expansion in the size of cities, resulting in motorized commute mode becoming increasingly prevalent among residents of large cities. However, the sedentary status of motorized commute mode has led to a reduction in daily activities for residents, which has a negative impact on their health. Using smart-phone application to gather commuting data from residents of Xi'an, and using the path analysis method, this study assessed people's physical health using the body mass index (BMI), and proposed a theoretical framework to analyze the urban built environment's direct, indirect, and total effects on residents' BMI mediated by motorized commute mode. The model result reveals that the built environment of work-residential areas, encompassing land use mix, building density, population density, number of bus lines, and proximity of subway stations, can significantly and indirectly impact BMI mediated by car driver, electric vehicles, and commuter shuttles. However, these factors do not significantly impact BMI through the use of buses and subways. The built environment has a significant direct impact on BMI as well, with the built environment of residential area having a greater influence than the workplace while mediating by car driver. The variation in the workplace's built environment variables will result in a change in BMI, mediated by different commuting modes. However, the population density of the workplace location, the distance between the workplace and city center, and the presence of colleges and universities in the vicinity may have an opposing effect. Therefore, it is proposed that the optimization of the built environment in occupational and residential areas can be gradually promoted through targeted renewal. This, in turn, can improve the health of residents. Corresponding policy suggestions include optimizing the layout and spatial structure of urban land, promoting the mixing of functions of land use near the workplace, and establishing an effective slow travel system.