本文旨在基于英语国家语料库，从系统功能语法角度分析介词in的功能用法。 在我们的日常交流中，介词扮演扮演着重要的角色。它们虽然数量小且有限,共计约一百个,但其在英语学习中的作用是绝不容忽视的。结果表明, 在五十个英语高频词汇的列表上，介词排在最前列。 学者已经从不同的角度对介词进行研究,比如语法和认知语言学。也有基于语料库的介词研究。然而,几乎没有从韩礼德的系统功能的角度来研究过介词,更不用说结合系统功能语言学和语料库。 本文选择其中一个常用的介词,in作为研究对象。基于语料库BNC,本文将检索出一万个实例，剔除一些无用的例子，并研究介词in的语法功能,根据环境成分的九种分类，即，跨度、位置、方式、原因、或然、伴随、角色、内容和角度。因此,本文将尝试根据过程和环境因素对介词in进行分类。通过结合系统功能语法和语料库，本文不仅显示一个新的研究视角,也根据九种环境成分，对介词in的语法功能进行了划分。本文不仅计算了各个类别的出现频率及百分比，还使用独立样本T检验来分析使用最多的环境成分处所和所有环境成分之间的显著性差异。同时，一万个实例使得研究更有代表性且更客观。 本文得出以下结论：首先,介词in功能使用频率的总体布局显示，介词in主要用于表示位置环境；第二，表达处所的环境成分与介词in的一般功能用法之间存在着显著差异；第三,虽然介词in主要用于表示位置环境,它也用于其他八个环境成分。相比其他介词只能表示仅有的几种环境成分,介词in几乎存在于所有的环境成分中；第三,在分析数据和把介词in划分在九种环境成分时,我们发现一些功能成分的界定十分模糊，这增加了识别环境成分的难度。 本文根据九种环境成分，对介词in的语法功能进行了划分。希望未来有更多的学者从系统功能语言学角度，并更广泛深入研究介词in。

This thesis aims to discuss the grammatical functions of preposition in from the perspective of Systemic Functional Grammar, based on the British National Corpus (BNC). Prepositions play an important role in our daily communication. Though the number of them is small and finite, totaling about one hundred, they can not be ignored in English. It is said that prepositions rank top in lists of fifty words that are the most frequently used in English. Prepositions have been studied from different approaches, such as grammar and cognitive linguistics. There are also studies based on corpus. However, prepositions are hardly discussed from the perspective of Systemic Functional Grammar, let alone combining Systemic Functional Grammar and corpus. This thesis chooses one of the frequently-used prepositions, in, as the focus. Based on the corpora BNC, this thesis will retrieve 10,000 instances, with some useless data excluded, and study the grammatical functions of preposition in, by classifying them into nine types of circumstantial element, namely, extent, location, manner, cause, contingency, accompaniment, role, matter, and angle. Overall distribution of occurrence and percentage is presented. Besides, independent samples t-test is used to discover the significant differences concerning the use of circumstance between the highly-used category, Location and the whole seventeen sub-categories. By combining Systemic Functional Grammar with the corpus approach, this thesis presents a new perspective of the studies for prepositions. 10,000 instances are collected, thus making the study more representative and objective. This thesis yields the following major findings. First, the overall distribution of frequency of in shows that in is mainly used as a circumstantial expression of Location. The other circumstantial elements account for a few percentage. Second, there is a significant difference between expressions of Location and the general grammatical functions of in. Third, although in is mainly used in the function of Location, it is also used in other eight categories. Compared to other prepositions, which just function as several types of circumstantial element, in is found in almost all categories. Fourth, when analyzing the data and classifying the nine circumstantial element, we find that some functions are quite ambiguous, thus making it hard to identify circumstantial elements. The research classifies the grammatical functions of in according to types of circumstantial elements. It is hoped that more researchers will further investigate the grammatical functions of in from the perspective of Systemic Functional Grammar in a broader scale.