Primary central nervous system lymphoma (PCNSL) is a highly aggressive malignant lymphoma. As most chemotherapy drugs have difficulty in crossing the blood-brain barrier, PCNSL shows a difficulty in clinical treatment, a high recurrence rate and a poor prognosis. Early identification of relapsed patients and prompt initiation of salvage therapy play a critical role in the improvement of patients' prognosis. Brain biopsy is the gold standard to identify recurrence, while the risk of operation failure and complications is still high. Non-invasive imaging techniques are beneficial for early identification of recurrence in PCNSL and can provide an important basis for guiding relapsed patients to adjust treatment plans in time. However, there is no unified evaluation standard for imaging methods of monitoring the relapsed lesions of PCNSL. With the further research of the pathophysiological mechanism of PCNSL, biomarker detection has become a new method to identify recurrence and more clinical evidence is still needed in the future.