摘要：Public ad is one of the components in the language construction with the using of language and words. The paper applies the social linguistic method, taking public ads in Beijing, Guangzhou, and Xinjiang as the study case. The result shows that standards of public ads are not varied. And there are many problems to be solved. First, the paper will have a review of the papers concerned with the topic. Secondly, the part is to talk about the functions of the signs, the classification of public ads, and the application of public ads. Thirdly, the paper is about the problems language application in the public and the analysis of the pubic ads. Lastly, it is the suggestion about the overall application of the bilingual language pubic signs--the English signs in cities in china.