Abstract In this paper, an alternative digital redesign approach dealing with the digital-controller-based input time-delay system is proposed. It directly converts the original continuous-time quadratic cost function into the discretized form and solves the optimization problem in the discrete-time domain. This method reveals an essentially different approach of digital redesign from the traditional ones. The main goal of approximation of the system performance of the discretized system to the original continuous-time one is achieved. Illustrative examples are presented to demonstrate the effectiveness of the proposed procedure.