How much percentage of plagiarism is allowed for the acceptance of research paper?

In my point of vier the Answer is Zero. However, it depends on what you mean my "plagiarism". Do you actually mean referencing the work of others? If so then it is simply a matter of citing your sources and using quotations whenever you quote others. You should use the work of others' sparing and only to support your own argument though. Your voice must be clear and distinct. I highly recommend using a service like Plagiarism Checker to evaluate the similarity index of your content to your sources.