Abstract: Objective To investigate effect of simulated saturation diving on immune function of T lymphocyte in mice.Methods Thirty Kunming-race mice were randomly divided into 5 groups:control group,at 100 m simulated saturation diving exposure for 24 h and 72 h groups,at 400 m simulated saturation diving exposure for 24 h and 72 h groups,each group for 6 mice.The T lymphocyte subsets of peripheral blood,collected 10 minutes after exposure,were assayed by flow cytometry.Results The level of CD4+ lymphocyte and CD4+/CD8+ ratio tended to increase after exposure at 100 m,while the levels of CD4+ lymphocyte and CD4+/CD8+ significantly decreased after exposure at 400 m.Conclusions The effect of simulated saturation diving on cellular immune function was correlated significantly with exposed pressure.