Abstract This paper describes the development of a mathematical model to predict the performance of multi-stage flash (MSF) plant systems under transient conditions. The model developed is based on coupling the dynamic equations of mass, energy and momentum. These equations describe the dynamic behavior of brine and product streams within the flashing stages, the effect of salinity and temperature variation on the specific heat, boiling point, enthalpy and density is accounted for in this model. The model which consists of a set of differential and algebraic equations (describing the dynamic behavior of each stage in terms of some key physical parameters) are solved by using the fifth order Runge-Kutta method. The proposed model was validated by using data from previous theoretical studies as well as actual data obtained from an operating MSF plant. The results obtained are useful for dynamic parametric studies and for the prediction of the performance of a given plant under a wide range of possible transient conditions.