The invention discloses a phase difference based kNN fingerprint localization algorithm. The phase difference based kNN fingerprint localization algorithm includes the steps of: acquiring phase difference data by using the RFID technology, and removing invalid information through data cleaning; eliminating abnormal data through data filtering; establishing a phase difference correction model and correcting the phase difference to obtain an accurate phase difference; and locating the corrected phase difference by using the kNN algorithm. The RFID technology is adopted to obtain the phase difference. The RFID a flexible application technology that is easy to handle, simple and practical, and especially suitable for automated control. The phase difference is corrected by the correction modelto make the obtained phase difference more accurate. The kNN algorithm is used to locate a tag to be tested. The kNN algorithm has a simple idea, a mature theory, and high accuracy, and can achieve accurate localization of position coordinates of the tag to be tested.