语言在当今的社会，政治，经济和文化生活中起着至关重要的作用。语言学家一直深耕于揭示语言的奥秘。批判性言语分析由福勒提出，试图揭露语言，权利以及意识形态之间的关系。批判性言语分析能够被用来分析众多文本，其中包括政治语篇。通过演讲，政治家们可以传达他们的想法，试图去影响他人的意识形态和获得他人的支持。近年来，许多研究者对美国总统的政治演讲进行了批判性言语分析。然而，大多数学者关注一位总统的演讲或者只关注总统在本国的演讲。少数学者对两位总统进行比较分析，少数学者关注到其它外交场合。因此，本文关注到了联合国总统演讲。联合国演讲的观众是全世界的领导人。本研究采用韩礼德的系统功能语言学来对演讲进行批判性言语分析。分析的内容为奥巴马和特朗普就任后第一次在联合国大会上所做的演讲。从三大元功能的角度出发，本文研究了两位总统演讲中的及物性、语气、人称代词、情态动词以及标注性主位的语言特点。在分析了两位总统演讲所体现的语言特点之后，又进行了对比分析。研究发现，在外交场合，政治演讲具有一定的规则性。此外，两篇演讲的语言可以折射出两位总统从政前的不同背景和经历。而政治家如何通过语言特点来展示他们的意识形态，实现政治目标也由此得到体现。

Language plays an important role in today’s social, political, economic and cultural life. Linguists have been researching and investigating this field, trying to explore the science of language. The Critical Discourse Analysis is proposed by Roger Fowler and aims to unveil the relationships among language, power and ideology since language is indispensable in social interactions. It is an efficient approach to analyze nearly all the discourse, including political speeches as the politicians spread their thinking, intend to influence others’ ideologies and win the support from the listeners. Recently, many researchers pay heed to the critical discourse analysis of American presidents such as Obama and Trump. However, most of them are concerned with one president and discourses such as the inaugural speech. Few of them do the comparative analysis between the two presidents or focus on diplomatic occasions. Therefore, this thesis pays attention to the president’ address in the Union General Assembly where the audience are the people all over the world. This thesis employs Halliday’s Systemic Functional Grammar to analyze Obama’s address in the 64th UN General Assembly and Trump’s address in the 72nd UN General Assembly, which are the first speech that they published in this place after taking the office. From the perspective of three meta-functions, this thesis analyzes the transitivity, mood structure, personal pronouns, modal verbs and marked theme of the two addresses. After summarizing the linguistic features of two presidents, this thesis also makes a comparison and contrast. Through analyzing, this study finds that there are principles of political speeches. Besides, the language of the two addresses can reflect the different background and experiences of the two presidents before they took the office. Thus, how politicians apply the linguistic features to show their ideology and realize their purposes is exposed.