In this paper, an optimal preview controller design method for a type of nonlinear discrete-time control systems is proposed. Firstly, based on the idea of the direct control method of nonlinear control system, the part of nonlinear feedback is taken as the formal input in order to make the nonlinear system into a“formal”linear system. Then, for this linear system, an optimal preview controller is designed by using the basic methods in the optimal preview control. Finally, by the application of the relationship between the formal input and actual input, the optimal preview controller for the nonlinear discrete-time system is obtained. It is also proved that the close-loop system is asymptotically stable if the formal linear system satisfies the stabilization and detectable conditions. The simulation results show the effectiveness of the proposed controller.