With the advancement of the internationalization of China’s higher education, the second classroom, as a core carrier for international students’ cross-cultural adaptation, has become increasingly prominent in importance. Taking Ningbo University as a case, this study systematically explores the current situation, challenges, and underlying causes of international students’ participation in the second classroom from the perspective of cross-cultural adaptation theory through questionnaires and in-depth interviews. The research finds that international students at the university have a high participation rate in the second classroom, achieving remarkable results in improving language proficiency and deepening cultural understanding. However, there are four core problems: one-way cultural display, lack of language support, imbalance between universalization and personalization in activity design, and fragmented information dissemination. The root cause lies in the failure of activity design to fully reflect the two-way, complex, and process-oriented characteristics of cross-cultural adaptation. Based on this, this paper proposes optimization strategies for constructing a “two-way integration” second classroom model, including promoting the transformation of activity content from “cultural display” to “cultural co-creation”, establishing a hierarchical and classified language support system, implementing customized management based on precise demand profiling, and building a multi-dimensional collaborative support network. It aims to provide theoretical reference and practical paths for universities to optimize the second classroom system for international students.