Abstract: Cellular immunity is an important part of human immune system, mainly mediated by CD8+cytotoxic T cells and CD4+ helper T cells. CD4+T cells include many subsets, for example, Th1 and Th2 cells, and the newly discovered subsets include Treg, Th17 and Th9 cells which are all involved in the tumor immune reaction at different degrees. But the mechanisms of inhibiting or promoting tumors remain unclear. This review collected the latest information of CD4+T subsets in malignant pleural effusion, including their changes, the possible mechanism, their roles in the tumor immune reaction, and provided a new targets for diagnosis and treatment of tumor.