Abstract: The Variable Structure Control（VSC） of discrete time system use discrete reaching law is discussed.The cause of the system’s chattering is analyzed.Combine with global sliding mode，a new discrete reaching law is given.The simulation results show that the arithmetic is feasible.It can reduce the systems chattering and make the stability from the beginning.

Key words: discrete time systems, chattering-free, Variable Structure Control（VSC）, discrete reaching law, global sliding-mode

摘要： 针对离散时间系统的变结构控制问题，对常规离散变结构抖动产生原因的分析，结合全程滑态变结构算法，给出了改进的离散趋近律。仿真结构表明，该方法是可行的，减小了系统的抖动，并从一开始就保证了系统的稳定性。

关键词: 离散时间系统, 变结构控制, 无抖振, 离散趋近律, 全程滑态