Abstract: Through hidden observation，the author of this paper investigated the administrative service centers of Chaidian District and the Wuhan Economic and Technological Development Zone. It is found that the staff in both centers use Mandarin more often when receiving citizens than when passively responding to questions. From the perspective of genders，both centers have experienced a higher frequency of using Mandarin among the male than the female to a balanced situation. Mandarin was less used among the middle and older aged than the young at the beginning，and later all staff are able to use Mandarin. This change greatly benefits from the vigorous popularization of the national language policy，the positive promotion of local policies，and the enhancement of citizens’language awareness as well.

Key words: urbanization, administrative service, code switching, Mandarin, dialect, Wuhan dialect