词类转换是英汉翻译中一种比较常见的翻译策略，已有研究仅从英汉语言差异的大背景来解释是不够的。本研究以原型理论为分析工具深入探讨英汉翻译过程中的词类转换的动因、机制和翻译策略问题。分别从范畴转换、语法化和语义转换上的原型观等三个方面对英译汉过程中词类转换的深层次动因作了阐释，尤其从语法化的视角对英语介词的翻译方法、动因以及英语冠词和单位名词的翻译机理作了具有前瞻性的探讨。

Part-of-speech transformation is a relatively common translation strategy in English-Chinese translation. Existing studies are not enough to explain the phenomenon just from the background of differences in English and Chinese languages. This research uses prototype theory as an analysis tool to explore the motivations, mechanisms and translation strategies of part-of-speech transformation in the process of English-Chinese translation. It interprets the deep motivations of part-of-speech transformation in the process of translation from English to Chinese from three aspects: category transformation, grammaticalization and semantic transformation. It made a prospective study of the translation methods, motivations of English prepositions especially from the perspective of grammaticalization and of the mechanism of English articles’ and unit nouns’ translation.