Stability control for a class of single-input single-output （SISO） uncertain nonlinear system with lower triangular struc- ture was studied. Cascade control with active compensation based on the backstepping approach was proposed. The designed controller, with the characteristics of simple structure, controlled convergence rate and good robustness, achieves the asymptotic stability of a closed-loop system. To solve the uncertainty of the closed-loop system, a new observer was designed to track the uncertainty in time. The stability of the closed-loop system is proved by introducing the singular perturbation theory. Simulation results show the effectiveness of the control method.