In the process of the competition between Mandarin and dialect, they are not simply replaced and be replaced, but permeate and integrate with each other. This paper addresses Mandarin and dialect diglossia phenomenon caused by the contact between them, including dialect mingled by Mandarin; Mandarin mingled by dialect. Mandarin and dialect diglossia are the result of the combination of internal and external factors, and it manifested in the three aspects of phonetic, vocabulary and grammar. The phenomena of dialect mingled by Mandarin and Mandarin mingled by dialect are widespread, and they are developing towards the direction of strengthening and weakening respectively, indicating that the living space of Mandarin has gradually developing and expanding, while dialect is gradually degenerating.