Resources and environment are essential elements of social and economic development. Whether the current resources and environment can sufficiently support economic and social development is an important scientific issue. Existing studies have not reached a consensus on the definition, assessment, and forewarning methods of resource and environmental carrying capacity (RECC). Therefore, this study puts forward a ternary theoretical system of RECC from the perspective of pressure, support, and adjustment, constructs a novel evaluation indices system of RECC, introduces a ternary evaluation model, and proposes a hierarchical forewarning method of RECC with a threshold of 1. Furthermore, an empirical demonstration of 31 provinces in China is presented. The results show that: (1) the average RECC index of 31 areas revealed a downward trend from 2012 to 2021, indicating the gradually improving RECC; (2) the RECC indices of central areas were always high, which manifests the poor RECC; (3) the number of provinces with RECC at Alert Level III decreased from 18 to 7, and the number of provinces at Non-Alert Level increased from 6 to 8.