The stability of input-output and internal states of multi-input systems with parameter perturbations and external disturbance is investigated. Two model transformations are adopted to realize the decomposition of input-output and internal states. By using the Lyapunov stability theory, the mathematical relationship between the convergence region and the uncertainties is formulated. A smooth nonsingular terminal sliding mode control method is proposed. The virtual control item is introduced to increase the relative order, and the robust differentiator is used to get derivative, so that the free-chattering sliding mode control is realized. Simulation results show the effectiveness of the proposed method.