Abstract: Taking Churchill's Memoirs of the Second World War and the translation version published by Yilin Publishing House as the data, this paper makes a detailed discussion and analysis of the phenomena on translation omission and mistranslation,improper choice of words and discourse incoherence in Yilin's translation.The analysis is carried out within the theoretical framework of situational context and three metafunctions put forward by Halliday.The conclusion of this paper is that a correct understanding of the semantic connotation of the situational context of the original text makes the greatest contribution to a highquality translation version,since it not only paves the way for a correct understanding of the deep semantic ideational connotation of the original text,but also provides an objective and powerful guidance both for transferring the equivalent interpersonal evaluative meaning of the words in the source text and for breaking up long sentence into short clauses and adjusting them in a logical manner,all of which are considered to be the most important issues for translators to pay attention to in the process of translation.