Authenticity is the unique advantage of Chinese timehonored brands. In the current fierce market competition environment, the renewal of timehonored brands has become particularly important. In the process of laozihao brand renewal, will the renewal strategy have a negative impact on the inherent advantages and attributes of laozihao brand? This problem is urgent to be discussed in theory and in practice. Based on the theory of organizational legitimacy, this study explores the influence mechanism of consumers perception of cultural differences on brand authenticity in the advertisements of timehonored brands adopting popular culture. The empirical study collected a total of 631 valid data from three timehonored brand advertisements. The result of data analysis shows that in the brand advertisement of timehonored brands combined with pop culture elements, the difference between traditional culture and pop culture perceived by consumers has a significant negative impact on the advertising legitimacy and brand authenticity. Advertising legitimacy plays an intermediary role between cultural differences and brand authenticity in consumer perceived advertising. The consumers involvement in pop culture significantly reduces the influence of perceived cultural differences in advertising on the legitimacy of advertising, and the moderating effect of perceived cultural differences in advertising on brand authenticity of pop culture involvement plays a role entirely through the legitimacy of advertising. The research results enrich the literature related to the field of brand authenticity and brand legitimacy, and have certain theoretical and practical significance.