In the Loess Plateau, natural resources are scarce and the ecological environment is fragile. Sustainable development requires special attention paid to resource and environmental carrying capacity (RECC). This paper selects 24 representative cities in five natural areas of the Loess Plateau, uses the entropy-weight-based TOPSIS method to evaluate and analyze the RECC of each city and region from 2013 to 2018, establishes a diagnosis model to identify the obstacle factors restricting the improvement of RECC and constructs the theoretical framework of RECC' system mechanism. Results show that the RECC of Loess Plateau is increasing in general but relatively small. The environmental and social subsystem have the highest and lowest carrying capacity respectively. There is an obvious contradiction between economic development and the environment. Population density, investment in technological innovation, per capita sown area of crops, and per capita water resources are the main obstacles affecting the improvement of RECC in the Loess Plateau. Such evaluation and diagnosis could support ecological civilization and sustainable development.