This paper is about the functional selection of linguistic units in order to reach translation equivalence. Linguistic units in this paper include morpheme/word, group, clause, and text under the perspective of Systemic Functional Linguistics (SFL). Translation involves two languages, i.e. the language that is translated (source language) and the language that is used to express the result of translation (receptor or target language). If equivalence is meant to be the same meaning in the two languages, and linguistic units are regarded parallel with linguistic forms, translation is then a process of pointing out the same meaning by means of selecting the appropriate linguistic forms. After a short review on the definition of translation, the concept of meaning, and the notion of equivalence, the paper presents how to do the selection of the linguistic units in translation and how the selection affects the meaning of the target text as the result of translation from the source text at the discourse level.