Abstract: In this pape,the robust output tracking control problem for nonlinear systems is discussed. The robustness against parameter uncertainties and unknown disturbances is considered.Here, the uncertainties do not satisfy the conventionai matching condition,We get a variable structure controller by constructing a Lyapunov function. It is shown that the overall states are bounded and the tracking errors converge to a residual set.A computer simulation is given,the results have verified the expected satisfactory performance.