The translation unit is a very important problem in translation studies．This paper classifies relevant studies into four groups: 1．translation unit does not exist; 2．functional linguistic method; 3．textual modification study method ( structural semantic method) ; 4． functional communication method．Based on that the thesis explore the novelty of Тюленев＇s research. Тюленев focused on translation process and paid attention to correspondence between original text and translated text in his translation unit studies． He considered Транслатема a translation unit and regarded the translation unit as a process． This point of view can not only improve the quality of translation in practice，but also point out new research approach of modern translation studies in theory．