This assignment analyses and researches the multilingual characteristics of Shanghai's local residents because of the controversial definitions of multilingualism. Under national language policy of Mandarin promotion, Shanghai dialect is in danger and should be cared for. It is a qualitative research based on the data from literature. From historical perspective, three languages frequently used in Shanghai are discussed and it turns out their connection of coexistence rather than competition. It also reveals that Shanghai indigenous residents are multilingual among Mandarin, Chinese and English.