The relationship between the spectral radius and the decay rate for discrete stochastic systems is investigated. Several equivalent conditions are obtained, which guarantee a specified decay rate of the closed-loop systems. Based on the relationship, this paper provides a design method for state feedback controllers, which ensure that the closed-loop systems converge as fast as possible. Finally, a numerical example is used to illustrate the developed method.where the diffusion term in dynamics depends on both the state and the control variables. The H ∞ model reduction problem was studied in [5] for both continuous and discrete stochastic systems, in which necessary and sufficient conditions for the solvability of the problem were obtained in terms of LMIs and a coupling non-convex rank constraint. In [6], a controllable set of a class of nonlinear stochastic control systems was characterized using optimal control theory of diffusion processes. Linear-quadratic optimal control and filtering problems have been solved for linear, weakly coupled continuous stochastic systems composed of N subsystems in [7]. Delay-dependent stability in the mean-square sense has been studied for stochastic systems with time-varying delays, Markovian switching and nonlinearities in article [8]. Basic theory and applications can be found in the book by Meyn and Tweedie [9] on Markov chains evolving in discrete time and on general state spaces.Stability and stabilization of stochastic systems have been studied extensively by many researchers. Some necessary and sufficient conditions were obtained via stochastic algebraic Riccati equations and LMIs in [4,10]. The problems of absolute stabilization and minimax control were investigated in [11] in the context of uncertain stochastic systems, while the issue of decentralized stabilization for a class of interconnected stochastic nonlinear systems was addressed in [12]. Characterizations of stability radii of a stable linear stochastic Itô system with respect to structured multi-perturbations were presented in [13]. Four types of definitions of exponential stability in the mean square are discussed for a more general class of discrete-time linear stochastic systems in [14], and they are equivalent for the system considered in this paper.This paper is organized as follows. Section 2 describes the problem studied in this paper, and some necessary lemmas are also introduced in this section. Section 3 investigates the equivalent relationship between the spectral radius and the decay rate. It can be explained that the spectral radius is associated with the decay rate in the sense of convergence speed. Based on this result, an optimal controller is designed. Finally, Section 4 presents an illustrative example and Section 5 concludes the paper.Notation: Throughout this paper, R n , C n , R m×n and C m×n are, respectively, the n-dimensional Euclidean space, the n-dimensional complex vector space, the set of all m ×n real matrices and the set of all m ×n complex matrices. N denotes the set of natura...