The Fourth Plenary Session of the 20th Central Committee of the Communist Party of China proposed to enhance internal driving forces and provide stratified and categorized assistance to underdeveloped regions. Scientific identification of underdeveloped areas is the foundation for improving assistance mechanisms and achieving common prosperity. A framework for the endogenous development momentum of underdeveloped regions was constructed from three dimensions-economic growth, social development, and ecological environment-and nine indicators. Using the AF method, a stratified and classified analysis was conducted based on 1433 county-level samples in 2022. The research identified 413 underdeveloped counties and 112 deeply underdeveloped counties based on the criterion that there are five or more and seven or more indicators of shortcomings simultaneously. The contribution of economic growth, social development and ecological environment to the index of shortcomings decreases in sequence. Amongthem, economic aggregate and fiscal level are the main shortcomings in the category of economic growth, educational attainment is the main shortcoming in the category of social development, and green coverage is the main shortcoming in the category of ecological environment. Among the special types of regions, the degree of underdevelopment, from high to low, is as follows: national key counties for rural revitalization assistance, counties that have been lifted out of poverty, counties for ethnic minorities, counties with ecological functions, counties in old revolutionary base areas, and counties along land borders. The underdeveloped areas are mainly distributed in the western and central regions, with a small number also distributed in the east. It is suggested that stratification be carried out based on the degree of shortage of indicators, and classification be made according to the contribution of each indicator to the shortboard index, so as to formulate more precise assistance policies. The research conclusion provides a scientific basis for establishing a stratified and classified assistance system during the 15th Five-Year Plan period.