In this paper, a new method for designing the robust Discrete-time Sliding Mode Control (DSMC) is proposed. To this end, firstly, the regular form based sliding mode control is reviewed. Then, according to the notion of strong stability and using scaling matrices (similarity transformation), a new method for considering the stability of discrete-time systems in the presence of general uncertainty term (matched and unmatched) is developed. Above all, in this paper, a new method to design the robust sliding surface according to the notion of strong stability is proposed. This problem is studied for both cases which system is or is not “strongly stabilizable under state-feedback”.