There is no limit to the number of times CNKI can check for plagiarism. As long as you want to check for plagiarism, you can check for plagiarism as many times as you want. However, it should be reminded that a certain fee needs to be paid for each duplication check. Therefore, if it is not necessary, you can try to reduce the number of duplicate checks as much as possible.
In addition, it should be noted that if the CNKI duplication check is carried out in advance, there may be the possibility of early detection prompts, so it needs to be treated with caution. If the school has requirements for the number of plagiarism checks, plagiarism checks can be carried out according to the school's requirements.
Different duplication checking systems have different algorithms and databases, so the duplication checking results will also be different. It is recommended that you use paper series free plagiarism checking software such as paperfree and papertime to check the first draft of the paper. For the final draft, check it with the school's required plagiarism checking system to ensure that the paper meets academic requirements.