本文首先在前人的研究基础上探讨语气副词“居然、竟然”的区别，主要从历时和共时两个维度，以及语法的三个平面对其本体展开研究。其次，依靠HSK动态作文语料库和暨南大学中介语语料库收集信息，探究留学生习得“居然”和“竟然”出现的偏误及原因。在此基础上进行合适的教学设计，以期减少留学生学习中的偏误。

This paper first discusses the difference between modal adverb "juran" and "jingran" on the basis of previous studies, and mainly studies its ontology from two dimensions of diachronic   and synchronic, as well as three planes of grammar. Secondly, the HSK dynamic composition   corpus and BBC corpus are used to collect information to explore the errors and reasons of     foreign  students' acquisition of "unexpectedly" and "unexpectedly". On this basis, carry on the appropriate teaching design, in order to reduce the overseas student study error.