In this paper an approach is developed for predicting fluid viscosity, specially for its density dependence, by the balance of entropy production and entropy flow in an open system near the equilibrium stationary state. The expressions for entropy production and entropy flow are obtained by non-equilibrium statistic thermodynamic principle. So a formula is obtained for viscosity coefficient that gives a density dependence proportional to entropy derivative with respect to density. The proportional amplitude is found to be a simple function of temperature. The theory in some special cases is compared with theory models for viscosity such as Hildebrand fluidity model and the modified Enskog theory (MET). The model is verified by experiment viscosity of a number of fluids including rare gases, carbon dioxide and hydrocarbons, and found in good agreement with experiment data from literature in liquid, gas and supercritical region. The absolute average deviation is 4.20% for 11691 data points of 24 fluids.