This study aims at deriving a less conservative delay-dependent criterion for the robust H ∞ stability analysis of discrete-time systems with interval time-varying state delay. To this end, an appropriate Lyapunov-Krasovskii functional containing triple summation terms is established and a relaxed inequality approach is proposed to address the induced double summation inequality and to exploits novel relaxation variables for null sum terms. Three numerical examples are provided to illustrate the effectiveness of the derived stability criteria.