The optimal preview control for a class of time-varying discrete systems with input time-delay is studied. The
property of difference operator is used to differentiate the input time-delay and the desired previewable tracking. Then an augmented error system is constructed, which contains the desired previewable tracking, but not the input time-delay. Based on the related results from optimal control theory and preview control theory, a controller with preview feed-forward compensation is designed for the augmented error system. The high-order Riccati equation is transformed into a lower-order one with some manipulation of matrix partitioning. And the preview controller for the original system is obtained. Finally, simulation results show the effectiveness of the proposed method.