Based on English word-formation, this paper analyzes the two aspects of English vocabulary changes, that is the appear⁃ance of English new words and changes of the lexical meanings. And then it discusses teachers’professional competence required in language education. Professional competence includes professionalism, methodic ability and social ability, in which solid lan⁃guage knowledge is an important part of professionalism. The study shows that English teachers should be aware of the changes of vocabulary and keep on updating lexical knowledge and learn language systematically as well, in order to better improve their pro⁃fessional competence, and therefore optimize the teaching effect.%以英语构词法为基础，从新词的产生和词义的变化两方面分析英语词汇的变迁，进而探讨语言教育中教师应该具备的职业能力。职业能力包括专业能力，方法能力和社会能力。其中扎实的语言知识是专业能力的一个重要内容。研究认为英语教师应该意识到词汇的变化，持续地更新词汇知识以及系统地学习语言知识，以更好地提高自身的职业能力，实现教学效果的最优化。
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