Abstract
Legal English is a kind of English widely used in legislation and judicature in common law countries. As a branch of customary language, legal English has its own specific linguistic features. Based on the present achievements on stylistics, vague linguistics and forensic linguistics, this thesis is to do a systematic research on preciseness and vagueness of legal English by taking the following varieties of language as research object: the legislative language, the judicial language and the language in the enforcement of law. The methods adopted include: content analysis, comparison and documentation analysis.
Lots of people think vagueness in law is contra-scientific and they even suggest the removal of it. Concerning the present research situation, the author firmly believes that vague language, a necessary and rational supplement to preciseness of legal English objectively exists in legal English, vagueness can improve the flexibility of legal English, meet the demands of legislation and make legal language more humanity in some situations, yet, if it is not properly used, vagueness may have some negative influence as well.
Through a series of systematic analysis, the author concludes that preciseness and vagueness, essential qualities of legal English, are contradicted but united.

Keywords   legal English   preciseness   vagueness

法律英语指的是以英语为法律语言的普通法国家在立法和司法过程中所使用的一种语言，它作为一种规约性语言的分支，有其独特的语言特征及风格。本文以文体学、模糊语言学和法律语言学现有的研究成果为基础，并以立法语言、司法语言及法律实施过程中的语言为研究对象，拟采用内容分析法、比较法和文献法对法律英语的准确性及模糊性进行系统研究。
对许多人来说，法律语言承载的是一种强制性力量，模糊语言在法律语言中没有存在的空间，应该尽量避免或消除。然作者认为：模糊性语言是客观存在于法律语言中的，模糊性法律语言是对法律语言准确性的一个必要的且合理的补充。模糊性不仅可以提高法律英语的灵活性，满足立法的需求，还能使法律语言在某些情况下变得更加人性化，但使用不当的话，法律英语模糊性也会产生一些消极影响。
通过一系列系统的论证，作者指出：准确性和模糊性都是法律英语的重要属性，二者是对立统一的。

关键词  法律英语   准确性   模糊性

1 Introduction
With the development of world trade economy, in especial after China entering WTO in 2001, the trade between China and other countries has been enlarged rapidly, so the mutual communication on law has been increasing greatly. Beyond all question, it is necessary for judges, learners and lawyers of legal English to understand and grasp the quintessence and characteristics of legal English. Nevertheless, there are few books and articles on this aspect, and the analysis is neither integrated nor concrete, hence this thesis is to do a systematic research on the characters of legal English.