The middle-income group is the pillar of economic development, the cornerstone of social harmony, and the foundation of an “olive-shaped” social structure. Efforts to increase the proportion of the middle-income group are crucial to implementing the people-centered development thought and ensuring that the broad masses of people share the fruits of reform and development. A review of China’s process of expanding the middle-income group since the founding of the People’s Republic of China shows that the expansion of the middle-income group is mainly achieved through the continuous improvement of internal and external economic accessibility and the consistent refinement of single-peak unbiased cohesive governance in the political sphere. Expanding the proportion of middle-income earners will remain a focus of China’s economic construction efforts. To this end, it is necessary to continue improving economic accessibility while ensuring the cohesion of political governance.