本文探讨介词在形成过程中词义虚化的方式及其语法特点的变化等问题。为此,考察了四个介词“沿、往、望、朝”的产生过程。这几个词都是在中古开始词义、词性的转化,至近代才成为介词的,词义虚化的线索有迹可循,语法特点的变化也比较清楚。在分析词义虚化的方式时,运用“义素”(sememe)概念,定义是最低层级上的词义构成成分。 This article explores the ways in which prepositions are defocused in meaning and the changes in their grammatical features. To this end, the study examines the four prepositions “along, toward, hope, and North Korea” generation process. These words are the beginning of the Middle Ages word meaning, the part of speech conversion, to modern times as a preposition, the trace of the word meaningless traces, the grammatical features of the change is also more clear. When analyzing the ways of semantic blurring, the concept of “sememe” is used to define the semantic components of the lowest level.