【Objective】To assay the expression of CD3~+、CD4~+、CD8~+ on T lymphocytes in patients with malignant carcinoma and investigate the relationship between T lymphocyte subset and the development and prognosis of malignant tumor.【Methods】APAAP methods were performed to detect the level of T lymphocyte subpopulation of 223 cases with malignant tumor and 220 cases of control group at the same time.【Results】The CD3~+、CD4~+、CD8~+T cell and the ratio of CD4~+/CD8~+ were significantly lower in patients than those in the control group(P0.01),while no significant difference of the number of CD8~+ T cell was found(P0.05).However,after treatment,the CD3~+、CD4~+、CD4~+/CD8~+ increased dramatically.【Conclusion】So to detect the value of CD3~+、CD4~+、CD8~+T cell and the ratio of CD4~+/CD8~+ can reflect the immunological state of malignant tumor patients and also there is some clinical value in estimating the prognosis of those patients.