Abstract:This thesis aims to explore how interpersonal meanings are realized by Mood System in English public service advertising (PSA) discourse. Halliday is the initiator of Systemic Functional Grammar (SFG), and SFG plays a very important role in various discourse analyses. Halliday’s interpersonal function is the function of interaction of people. Mood system as a way of realizing interpersonal meaning is a great tool to analyze discourses.

　　　As one kind of non-commercial advertising, public service advertising is used to inform and educate the public by the way of various media, which aims to maintain social morality and achieve the sustainable development in harmony with nature. Nowadays, the majority of the studies focus on commercial ads, but few on PSA, especially from SFG perspective. Therefore, this thesis explores how PSA realize interpersonal meaning by mood system through different syntactic patterns. 

　　　The research finds that in English PSA texts, the advertiser uses declarative, interrogative and imperative to realize different purposes of the advertisements (giving information or command). Therefore, all these perspectives of mood system in the realization of interpersonal meaning in PSA can have many functions. They can help to attract the audience’s attention. They can strengthen the persuasiveness of the content of the advertisement, and build the intimate relationship between the advertiser and the audience and thus stimulate the audience to take positive actions and solve the social problems with other people.

Key words: mood system; English public service advertising; interpersonal meaning；syntactic patterns

摘要:本文探讨了英语公益广告语篇中人际意义的表达。韩礼德是系统功能语法的创始人，而系统功能语法在不同语篇的分析上发挥着重要的作用。韩礼德的人际功能是人们相互作用的功能。语气系统作为实现人际功能的一种方式是分析语篇的重要工具。

　　　公益广告是一种旨在通过各种媒体向社会公众进行宣传和教育，以维护社会道德和正常秩序、实现人与自然和谐永续发展的非商业性广告。目前对广告的研究大多集中在商业广告，对于公益广告的研究则相对较少，而运用系统功能语法对公益广告语言的研究则更加少见。因此本研究以系统功能语法为基础，看公益广告是如何从句法模式角度通过语气来实现其人际意义的。

　　　研究发现，在英语公益广告语篇中，广告者经常采用陈述语气、疑问语气、以及祈使语气来实现广告的不同目的（给予信息或是命令）。所以，在英语公益广告语篇中，语气系统有助于吸引观众的注意力，增强广告内容的说服力，使广告者和观众建立密切的关系，从而激励观众采取积极的行动，共同解决社会问题。

关键词：语气系统；英语公益广告；人际意义；句法模式