Chronic active Epstein Barr virus infection(CAEBV) is subcategorized as EBV⁺ T/NK lymphoproliferative diseases (EBV⁺ T/NK-cell LPD) and characterized by recurrent or chronic symptoms of infectious mononucleosis and clonal expansion of EBV⁺ T/NK cells and with high morbidity and mortality in clinic. It remains unclear what is the cause of CAEBV due to its complexity among different cases. Clinically, it is of importance to give accurate classification of EBV⁺ T/NK-cell LPD for appropriate therapeutic strategy, however, the standards for classification are still unsettled and the treatments are less than satisfactory. To explore some clues for further study, the current understanding of the pathogenesis of CAEBV will be summarized from several aspects such as the clonal expansion of EBV infected cells, EBV related virological factors, defects in host immune system in this review.