Abstract: Objective To investigate the effect of long term occupational exposure on the immune function of workers of a power plant. MethodsAn exposure group of 200 workers in a power plant and a control group of 80 normal people of health checkup were examined for their cellular immunity and humoral immunity by flow cytometry instrument testing technology of the United States BD company and immune turbidimetric method. ResultsThe abnormality rate (16.5%) of immune globulin in exposure group were significantly higher than that (7.5%) in control group (P<0.01). The values of CD3, CD4, CD8 positive T-lymphocytes and the ratio CD4/CD8 were significantly lower in exposure group than those in control group (P<0.05). The levels of IgG and IgA in exposure group were significantly lower than those in control group (P<0.05). ConclusionIt is indicated that long term occupational exposure in power plant may lower the values of CD3, CD4, CD8 positive T-lymphocytes and the ratio of CD4/CD8 and reduce the function of humoral immunity.