Significant advances have been made in adopting the linear systems theory in modeling the rainfall-runoff process since Nash proposed the model with equal reservoirs in series in 1957. Such hydrologic models, known as input-output models, are attempted to establish a causal linkage between two or more observed phenomena without detailed description of the physical process under investigation.Continuous models mayebe handled elegantly with operational mathematics. However,hydrologic data are almost always discrete.Therefore, discrete models are of general interest in practice.The purpose of this paper is to present a discretely coincident form of general linear hybrologic system models, to describe some important properties of discrete, linear, hydrologic system model and to suggest different methods for estimating paramters with numerical examples.