The influence of brand personality on brand extension has been studied, but there are few studies on whether and how brand extension affects brand personality. Taking Yunnan Baiyao, a time-honored brand in China's pharmaceutical industry as the research object, an exploratory study on the brand personality of Yunnan Baiyao was conducted. Firstly, the project vocabulary of Yunnan Baiyao brand personality was determined through four qualitative studies, and then the three brand personality dimensions of Yunnan Baiyao brand personality were determined through exploratory factor analysis of 353 samples obtained through questionnaire survey. That is, the classic was sincere, reliable, safe, unique and mysterious, and completed the measurement of the brand personality of products in the pharmaceutical field. On this basis, theoretical hypotheses on how Yunnan Baiyao's brand extension to daily chemical products affects its brand personality were put forward. 205 samples were obtained through questionnaire survey, and the hypothesis was tested by regression analysis. It is found that the two dimensions of brand extension, emotional extension and functional extension, have a significant positive impact on brand personality, However, the positive impact of functional extension on brand personality is more significant, and the effects of functional extension and emotional extension on all dimensions of brand personality are different. The research conclusion adds a new perspective to the feedback effect of brand extension.Some suggestions are provided for enterprises to determine the boundary of brand extension.To form the positive feedback effect of brand extension on brand personality, it is necessary to reasonably divide the category attributes of each extended product, and pay attention to the functional extension of the brand on the basis of ensuring the effect of emotional extension.