Extracorporeal photopheresis(ECP) is a bidirectional cellular immunomodulatory therapy based on leukapheresis, which can mediate not only immunopotentiation but also immunosuppression. Clinically, ECP has been observed to have good efficacy in the treatment of cutaneous T cell lymphoma(CTCL), graft versus-host disease(GVHD) and solid organ transplant rejection, also the US Food and Drug Administration(FDA) has approved ECP for the treatment of CTCL. The treatment guidelines for GVHD in the US and Europe also include ECP, however, there is a lack of relevant guidelines in China. Although the exact mechanism of ECP is not fully explained, recent studies provide a theoretical basis for a further understanding of the bidirectional regulation of ECP.The initial hypothesis was the combination of 8-methoxypsoralen(8-MOP) and ultraviolet A(UVA) to induce apoptosis of immune cells. As the research progressed, this idea was transformed into the differentiation of monocyte to dendritic cell(DC), cytokine alteration and the regulatory T cell(Treg) stimulation.In this article, the current exploration of the immunomodulatory mechanism in ECP and its clinical application were reviewed, also the latest molecular mechanism of ECP mediated immunopotentiation and immunosuppression was comprehensively analyzed, meanwhile the further promotion and clinical application of ECP in China had been prospected.