Abstract: The rapid development of the mobile internet technology has contributed to the increase in the internet user population in China. Mobile communication equipment has gradually become a common device for most internet users. Mobile social platforms have been favored by many users, and social e-commerce has shown a diversified development trend. As a new trend for consumers to participate in the value co-creation of social e-commerce, user-generated content will have an impact on the creation of corporate brand equity value, and it has practical value for the research on the co-creation mechanism of corporate brand equity value based on user-generated content. In addition, the academic research on value co-creation focuses on customer value, user participation, business model innovation, etc., but few scholars touch upon virtual brand communities and user-generated content. The value co-creation based on the user-generated content has potential academic research value. Through literature review of value co-creation theory, brand equity theory, and the concept on user-generated content, it can be found that user-generated content is a way for users to participate in the innovation in the digital economy era, which will have an impact on the generation of corporate brand equity value. Brand equity models, such as the Aaker model and the CBBE model, explain the influencing factors of brand equity from the perspective of consumers, and provide a reference for the establishment of a social e-commerce brand equity value co-creation mechanism model based on user-generated content. The model points out that the four stages of corporate brand equity are brand identity, brand connotation, brand response, and brand relationship. Each stage of the influencing factors have their own focus. In the digital economy era, consumer behavior will have an effect on enhancing the company's own brand effect. The SICAS model proposed by the Data Center of China Internet (DCCI) believes that users will generate five consumer behaviors in the social media environment, such as brand-user mutual perceiving, interest growing-interaction, connection-interactive communication, action-purchase and experience-sharing. Interactive sharing is an important part of users' participation in the innovation process. The corporate brand equity based on user-generated content has the following four characteristics: one is that social network has become a basic tool, the second is the integration of users and brands, the third is a mechanism for users to participate in value co-creation, and the fourth is the feedback circle which promotes brand value transformation. Evaluation, feeling, and sharing will have an impact on the corporate brand response. Interaction, as the last link of the feedback circle, has a positive effect on the corporate brand relationship. In order to verify the rationality of the model furthermore, the grounded theory is used to analyze the Xiaomi brand case. Through using NVivo 11 software, it's found that Xiaomi's culture on user's participation has laid the foundation for it to build its own brand equity. Xiaomi fans use Weibo, MIUI community and other online interactive platforms to deliver product information to Xiaomi. At the same time, they also send out recommendation signals to more potential users, which enables Xiaomi to obtain a better word-of-mouth effect with lower marketing costs, and the brand connotation became deeper, the brand response became stronger, and the brand relationship became more stable. Xiaomi collects users' opinions on products through social marketing, and transmits the information to its upstream suppliers to achieve personalized customization, and then production costs reduced, the brand identity became more prominent, and the brand connotation got deeper. The "brand equity value co-creation iron triangle" of Xiaomi dominated by interactive behavior shows that the user-generated content has a positive effect on the corporate brand equity value co-creation. It also shows that companies should change their cogitation and use interactive marketing through social network or other methods to strengthen corporate brand equity and achieve sustainable development.

Key words: social e-commerce, user-generated content, brand equity, value co-creation, Xiaomi