Based on the perspective of activity theory, this paper employs a qualitative approach to investigate a Miao English teacher with Miao Language as native language, Chinese as communicative language and English as the third language, to explore the characteristics and crisis of linguistic identity, as well as the way to eliminate the crisis. The results indicate that: (1) the stages, situations and contradictions are the three characteristics of linguistic identity; (2) there is a crisis of identity in linguistic identity; (3) the ways to eliminate the crisis of linguistic identity need to meet the five aspects, including the main body who with self-promoting consciousness, the effective intermediary tools, the positive community of practice, the strict norms and the positive social division of labor.