Abstract： Objective To investigate the effects of gradational simulated saturation diving on the cellular immune function of the divers.Methods Nine male healthy divers conducted simulated saturation diving gradationally at 65 m,250 m and 480 m.Blood samples were collected before and after each pressure exposure to detect changes in T lymphocyte subgroups of the peripheral blood,with flow cytometry.Results The level of CD4 lymphocytes and CD4/CD8 (41.26 ± 8.46、1.36 ± 0.50 ) ratio increased significantly following 250 m saturation exposure,when compared with those before dive ( 35.63 ± 7.93、1.04 ± 0.36).However,no significant changes were detected in CD4 lymphocytes of the peripheral blood,both before and after saturation exposure at 65 m and 480 m.For those divers who didn 't experience the 65 m saturation exposure,their immune function during the stage of the 480 m saturation exposure was more easily affected,when compared with that of other divers.Conclusions It seemed that gradational heliox hyperbaric exposure could protect the cellular immune function of saturation divers.