Abstract: In Lorenz chaos,the sign relation between coordinates "x" and "y" of a phase point determines whether the point can overpass the y-z coordinate surface or not,and it also determines in which wing of Lorenz attractor the point will stay.Through imposing small influence on "y" at given places the system can be made to have only one way to go and then it becomes periodic.Different kinds of periodic motion can be formed by imposing influence on "y" at different places.As a result Lorenz chaos can be controlled.The work illuminates that intrinsic random provides a good opportunity to control Lorenz chaos while it makes forecast difficult.