Abstract: The cyberspace based on the support of big data, artificial intelligence and other technologies has become a new space with very sovereign characteristics and ideological "preferences" and deeply embedded in people's daily life field, and spawned the "imitation" characteristics of the current cyberspace. It not only profoundly changes the self-existence, social relations, subject interaction and other life patterns of young people, but also marks the new positioning of cyberspace, that is, the new field of mainstream ideological identity of young people. However, the interweaving of the "imitation" picture of cyberspace with the "truth" myths such as fragmented presentation, diversified orientation and "decentralized" construction in the "post-truth" era has weakened the mainstream ideological identity of young people in cyberspace. Therefore, it has become an important aspect to strengthen youth's mainstream ideological identity and self-confidence in cyberspace to clarify the boundaries of youth's mainstream ideological identity in cyberspace through theme identification, figurative methods and environmental optimization.