Underground space resources (USR) are a new type of land resources with the dual attributes of resources and environment. The urban underground space resources (UUSR) are extremely precious, sensitive and irreversible resources which are carriers to the survival and development of modern urban. The development and utilization of UUSR must be scientific, in-order and reasonable. Besides, the assessment of UUSR is the basis and premise of UUSR utilization, unified control of national land space and three dimensional urban planning. In this study, the similarities and differences between land and mineral resources assessment, groundwater resource effect assessment and UUSR assessment are analyzed. The actualities, including progress and deficiency of UUSR assessment are discussed from seven aspects. The importance of strengthening UUSR assessment research and its connotation construction are discussed. Three key scientific issues of UUSR are discussed as the multi-scale effect of UUSR assessment elements, the mutual feedback mechanism between UUSR and its development and utilization, and the corresponding dynamic response of UUSR assessment elements. Meanwhile, the main contents of UUSR assessment are explored, and the future trend in five aspects are presented. Subsequently, the preliminary definition and corresponding concepts of the science of underground space resources (SUSR) are proposed. In addition, the basic framework and research paradigm of SUSR are presented.