This article investigates the relationship between bilinguals cultural identification and language proficiency and tries to find out the strategy to improve bilinguals language proficiency. It was written in a literature review format, summarizing ten articles about bilinguals, and comparing them to research the topic. The study mostly researches three bilingual groups: immigrants, heritage language speakers, and transnational students. Moreover, found that immigrants would either identify with both cultures or deny one of them. Their attitude toward the culture will also reflect their language proficiency; they either have balanced language proficiency in both languages or show a preference for one. For heritage language speakers, their cultural identification can be consolidated through involvement in a kind of cultural background; then, heritage language speakers would raise their willingness to improve their language proficiency of heritage language. Finally, the transnational students, if they can identify themselves as successful students, might hold more confidence to study the language and gradually get better proficiency. This article concludes with three directions to help bilingual people improve their language proficiency based on their cultural identification. This could be concluded as producing a better bilingual community, recommending HL speakers parents use more about their heritage language before their children, and helping bilingual students build the identification as successful students.