Robustness recovery and chattering reduction of the discrete-time quasi-sliding mode(D-QSM) are studied. A decoupled disturbance compensator(DDC) based robust D-QSM(RD-QSM) control method is proposed for a class of discrete-time systems with matched modeling error and unmatched external disturbance. In order to recover system robustness, an improved DDC is designed for unmatched disturbance. The estimation error of DDC is convergent and bounded. The power function(PF) is introduced in the improved RD-QSM control method, which can totally eliminate the chattering of system. The quasi-sliding mode band(QSMB) of the switch function is given. The D-QSM of the close-loop system is proved to be reachable and stable. Simulation results show the effectiveness of the proposed control method.