Underground pedestrian systems (UPS) have been developed worldwide especially in the central areas of mega cities. They are integrated with subway systems, underground shopping streets and malls, and the basement of department stores in various forms and integrated with commerce, transport, retailing and public usage in urban functions. In cities with severe weather conditions such as Toronto and Montreal in Canada, UPS provided a weather-controlled walking environment. In dense urban settings such as Tokyo, Japan and Shanghai, China, UPS provides a comprehensive usage of urban space that is comparable to that which occurs at the street level. The natural and built environments affect the utilization of UPS. Environmental factors are discussed to demonstrate how UPS have developed and functioned. Based on previous research, this paper has selected 19 cities as cases studies to explore the decisive factors of natural and built environments that have influenced UPS development specifically with regard to four aspects namely climate, subway construction, land usage and economic environment. The research revealed the extent of prevalence of these four aspects in cities and determined the differentiating factors of the natural and built environments that resulted in the establishment of UPS. SPSS was applied to test the differences between developing and advanced economies in relation to the prevalence of these factors.