A novel nonlinear disturbance attenuation control scheme based on Hamiltonian theory for the solution of structure preserving multi-machine power systems is proposed in this paper. The dissipative Hamiltonian realization of structure preserving power system is completed using the singular perturbation approach in which the algebraic equations are treated as a limit of fast dynamics; moreover, a nonlinear disturbance attenuation excitation controller is designed without any linearization treatment to improve the transient stability as well as the robustness of power system with respect to unknown exogenous disturbance on the system in the sense of L/sub 2/-gain. Simulation results on a 4-machine system demonstrate that the proposed scheme can obviously enhance the transient stability of the system regardless of the exogenous disturbance.