Abstract: The problem of the design of variable structure control for discrete-time systems is considered.A new discrete reaching law is presented to improve the reaching process of discrete exponential reaching law.The discrete-time variable structure control system designed by this reaching law can not only weaken the chattering and control the system state approach to zero diminishingly，but also keep the basic property of quasi-sliding mode which can cross the switching surface step by step.This method improves the reaching process and enhances the control quality of the control system.The simulation results validate the feasibility and reasonability of this method.

Key words: discrete-time system, variable structure control, discrete reaching law, chattering

摘要： 针对离散时间系统变结构控制的设计问题进行了研究。为了改善离散指数趋近律的趋近过程，提出了一种新的趋近律，利用该趋近律设计的变结构控制器，不仅能够大幅度削弱抖振，使系统运动最终趋于原点不存在稳态振荡，而且能使系统的准滑动模态保持步步穿越切换面的基本属性，有效地改善了趋近过程，提高了控制品质。仿真分析验证了该方法的合理性与有效性。

关键词: 离散时间系统, 变结构控制, 离散趋近律, 抖振