In this paper, a novel reaching law for discrete-time sliding-mode control system is proposed. In the proposed method, the proportional term is replaced by an exponential term that dynamically adapts to the variation of the sliding variable. The proposed reaching law in this paper has two merits, one is to ensure the stability and better robustness of the controlled plant than the existing approaches, and another is effectively eliminating undesirable chattering. And when the sliding variable tends to zero, the ultimate magnitude of the trajectory of system state around sliding surface in the proposed method is smaller than in previous approach. The simulation results validated the feasibility and reasonability of proposed method.