In order to understand relation between turning residual stress and time, there is a turning experiment with 40Cr sample in different experimental conditions. Residual stress, roughness and specimen diameter of samples were observed and analyzed to find out their change laws over time.The results show that after machined, the maximum turning residual stress is reduced with time, but change rate are gradually decreased with time and finally tended to stop change. Thickness of turning residual stress layer is reduced with time, but location of the maximum tensile stress and the maximum compressive stress do not change with time. Effects on roughness and size of workpiece are negligible when residual stress changed．