Abstract-In this paper, dynamical behaviors of the discretetime sliding-mode-control (DSMC) uncertain systems are studied. First, a discrete reaching law with a disturbance compensator is presented, and a sliding-mode controller is designed by using the proposed reaching law. Second, the time steps for the system trajectories to converge to the switching manifold are found. Then, a quasi-sliding-mode domain (QSMD) of the DSMC uncertain systems is obtained, and the system dynamics of the DSMC systems in QSMD are described. Finally, numerical simulations are given to demonstrate the effectiveness of the proposed strategies.