According to regulations of the Ministry of Education and Training, the requirement for students with a university degree is foreign language Competency Framework. To achieve level 3/6, student must take the Cambridge PET level test with 4 skills: Listening, Speaking, Reading, Writing. Among these 4 skill, Writing is considered to be the difficult one. ChatGPT is an AI tool with the ability to generate natural texts, opening up many opportunities for learning and improving Writing skill in many fields including Writing Part 3 level 3/6. In this article, we will consider the important role of ChatGPT in improving writing skill, provide detailed instructions on how to use ChatGPT in Writing Part 3.