Abstract: Stabilizing middle-income groups and unleashing their consumption potential is the only way for China to achieve common prosperity for all people, and it is also the practical need to overcome the middle-income trap and optimize the internal structure of middle-income groups. In this paper, the current middle-income group with the poor ability to withstand risks and develop sustainably, easy to be "off the shelf" to become a low-income group, is called "vulnerable middle-income group". The paper has found that under various standards, the proportion of vulnerable middle-income groups is on average close to half. From the perspective of space, vulnerable groups are mostly distributed in the western and central southern regions; from the economic perspective, low property income, low transfer income, high operating income, and high health care expenditure are the significant characteristics of vulnerable groups. Low educational level, heavy child support burden and medical expenses are important factors inducing vulnerability. In the future, efforts should be properly handled on the relationship between "stability" and "expansion", focus on the main line of accurate identification and classified policy implementation, and focus on urban settlement, education, housing and social security to gradually improve the stability of middle-income groups.