This paper introduces the concept of consumer vulnerability and builds a nonrational purchase behavior model to improve consumer welfare. On this basis, through the review of the research status of consumer vulnerability, this paper redefines it and develops the consumer vulnerability scale for the first time. The results of exploratory factor analysis and confirmatory factor analysis show that the reliability and validity of the scale are convincing. In addition, the data suitability indices of the first order factor model, as well as the second order factor model are both significant. The scale’s first order factor contains 7 dimensions, namely, product knowledge, product promotion, social pressure, refunds policy, marketing and emotional pressure, distinguish ability, and purchase ability; the second order factor contains two dimensions, which are knowledge-based vulnerability and powerlessness-based vulnerability. The empirical results show that the scale has certain predictive validity for nonrational purchase behavior and consumer welfare.