Abstract: Expanding the middle-income group is an important means to achieve common prosperity. Based on the definition and measurement criteria of middle-income groups, a statistical method to measure the share of the middle-income group using macro statistics is proposed and used to explore the inner pattern of changes in the size of the middle-income group. The paper measures the share and distribution characteristics of middle-income groups in 127 countries and regions based on the statistics released by the World Bank and focuses on the relationship between the share of middle-income group and the Gini coefficient, to summarize the reasonable share of middle-income group and the internal logic of expanding middle-income group in the context of common prosperity. The paper also measures the share of middle-income group and quantitatively analyzes its change effects using the data from 2003 to 2021 in China. Based on this, the practical path of expanding the middle-income group is analyzed to provide an objective basis for promoting common prosperity by expanding the middle-income group in the new development stage of China.

Key words: Common Prosperity, Middle-Income Group, Gini Coefficient, Income Distribution Patterns