Difficulty difference: level 6 > level 4. Band 6 listening is more difficult, vocabulary is bigger, and reading is longer and more complicated. Writing and translation are more demanding. Need more study and preparation.
Different object-oriented: CET-4 is mainly for non-English majors, while CET-6 is mainly for English majors. The boundaries are vague, and non-English majors also choose Band 6.
Social recognition is different: CET-6 has higher social recognition, and many employers require CET-6 certificates, especially international companies and institutions. Band 4 is considered as the basic proof of English proficiency.