In recent years, rapid global urbanization accompanied by rapid economic growth has resulted in increasingly serious eco-environmental problems such as land degradation and pollution. As a society, we are gradually realizing the role of environmental protection and ecologically-focused construction in promoting sustainable development. As an important method for assessing sustainable development, ecological carrying capacity (ECC) has become a powerful tool for investigating sustainable development and assessing eco-environmental problems. Based on results from a large number of previous studies in this discipline, we summarized and generalized the implications, main assessment methods, and key research domains of ECC. Deficiencies and future trends in ECC research are identified. In terms of implications, ECC can be roughly defined into the perspectives of environmental change, human effects on ecological systems, and holistic ecological systems. The primary assessment methods and models can be classified in accordance with these three perspectives, including ecological footprint method, ecosystem-services-based method, net primary productivity method, situation space method, energetic ecological footprint model, system dynamics model, and coupling model. We compared the advantages and disadvantage of different methods and analyzed their applicable conditions. As ECC research has advanced, related studies have gradually extend to land systems, watershed systems, ecologically vulnerable areas, tourism systems, and urban comprehensive systems, which have solved relevant eco-environmental problems based on ECC assessments. Currently, ECC research lacks a standard definition for the ECC index threshold, research related to dynamic monitoring and early warning, sufficient consideration of scientific and technological drivers, and spatial pattern analyses. Future trends in ECC-related research should provide a large-scale assessment of cross-border areas and ecological vulnerable areas, construct an ecological warning platform, and consistently analyze ECC and regional leading industries.