IELTS (International English Language Testing System) is a globally recognized English language test, which is used to evaluate the English language ability of people who intend to study, work or immigrate in an environment where English is the teaching language. The IELTS test not only tests candidates' language knowledge, but also emphasizes their practical communication ability, especially their ability to use English in academic and general training environments. It examines the comprehensive ability of listening, speaking, reading and writing, especially the scoring of oral English and writing. In addition, there will be real academic scenes and life dialogues in the exam, which requires candidates to be flexible in language use.

CET4-4 is an English proficiency test for college students in Chinese mainland, which mainly measures students' basic level of college English. Although it also covers listening, speaking, reading and writing skills, its difficulty design and assessment criteria pay more attention to the content of basic English education. The form and content of the exam are relatively fixed, and the oral part is not mandatory, which also meets the requirements of international language environment adaptability and complex language application scenarios.

To sum up, IELTS is generally considered to be more difficult than CET-4 because of its internationalization orientation, comprehensive language application requirements and strict grading system.