In this paper, modeling and simulation of high-pressure urea synthesis loop has been studied. The extended electrolytic UNIQUAC equation has been used to describe the nonideality of liquid phase of NH3-CO2-H2O-urea system under high pressure and high temperature, and the perturbed-hard-sphere (PHS) equation of state has been used to predict the vapor fugacity coefficients. The vapor-liquid equilibrium has been treated simultaneously with chemical reactions due to the complex features of the urea synthesis system. A concrete procedure for simulation of the key units and flowsheet of the high-pressure urea synthesis loop has been developed. The equilibrium-stage model has been applied to modeling and simulation of the urea reactor, CO2 stripper and other key units in the high-pressure loop for urea synthesis, and the simultaneous-modular approach has been adopted to simulate the flowsheet. The simulation results have been found to be in good agreement with the design data from the industry-scale plant. This work provides an effective tool and significant guidance for design or retrofit of urea synthesis process. (c) 2004 Elsevier Ltd. All rights reserved.