The design of street canyons has become a focus of attention under the requirements of high-quality urban modernization, while existing research has gradually broken through the basic norms of aesthetic design to include ecological considerations. However, it is only in recent decades that relevant research has been carried out in super and super-large cities in China. In this article, we take Nanchang, one of the largest cities in China, as an example, and use ENVI-met software (v5.5.1.) to simulate and analyze the street canyon of the city. Certain measurements were made and verified to compare the microclimatic conditions of street canyons at different scales. The relationship between street canyon morphology and outdoor thermal comfort was explored in terms of near-surface air temperature, wind speed, and thermal comfort indicators. The results show that there is a high correlation between the morphology of street canyons, such as orientation, aspect ratio interface continuity, and outdoor thermal comfort. Therefore, starting from adjusting the morphological characteristics of street canyons, practical suggestions can be provided for urban planners to guide the sustainable development of contemporary cities and improve the comfort of urban street spaces.