In this paper, the procedure of feedback decomposition synthesis, providing stabilization of output variables with the given accuracy is developed for a nonlinear control plant which model contains external unmatched disturbances and is presented in the input-output block form with stable inner dynamic. The approach provides restrictions on state variables during a control process by using smooth, bounded S-shaped sigma-functions as local feedbacks and does not require parametric certainty of the control plant and introduction of dynamic models of external disturbances.