As the scale of endangered minority place names increases in the agro-pastoral ecotone of northern China, the vulnerability of minority place names is becoming apparent. The place name is an open cultural system that is composed with many elements. Therefore, how to achieve the transformation from qualitative research on endangered minority place names to quantitative research on the degree of vulnerability from a systematic perspective has important theoretical and practical implications. Based on these, we introduced the theory of vulnerability, identified the factors affecting the vulnerability of minority place names based on long-term field investigation and literature review, developed a quantitative evaluation system, and clarified the evaluation scale and methods. Finally, quantitative results were presented through an empirical study in the Damao Banner, Inner Mongolia, China. The results of the empirical study show that the Mongolian place name culture in the case study area has prominent sensitivity and exposure, weak resilience, and obvious vulnerability. The vulnerability is jointly affected by internal damaging factors and external disturbing factors. Among these factors, the local people’s wrong perception of the etymology and meaning of Mongolian place names, the high popularity of Chinese and the social recognition of Chinese translations of place names, and the inaccurate translations of Mongolian place names are the key factors that make the Mongolian place name culture vulnerable. In addition, the simplification and non-standardization of words and sounds used in Chinese translation, the large number of mergers, changes and abandonment of Mongolian place names, the limited number of references related to place names, and the drastic decrease in the size of Mongolian user groups are important indicators.