A new discrete-time nonlinear exponentially approaching law is proposed to overcome the shortcomings of the traditional approaching law. A nonlinear function is adopted in the switching coefficients in the approaching law, to simulate the real situation that the distances of the switching coefficients from the system mobile point to the sliding surface decrease step by step, with the approaching speed improved and the chattering depressed, thus to improve the robust performance of the system indirectly. The simulation results show the superiority of the discrete-time approaching law, with better controlling performance for deterministic and non-deterministic systems alike.