Growing world population increases food demand. Reaction coupling between ammonia and urea synthesis provides insight in developing fertilizer production plant which is more energy efficient and which in turn enables abundant and cheap food production. The ammonia-urea reaction coupling is still a new field and requires simple and sufficient models to describe the system. Mathematical models derivation, simulation, constants tuning and validations were done using commercial software. Sufficient models were obtained for the future development of reaction coupling conceptual reactor. For urea synthesis reaction, the equilibrium carbon dioxide conversion is close to 80 and the equilibrium urea concentration is around 750 mol/m3 at the optimum operating conditions of around 450K and 12 MPa. The optimum range of NH3:CO2 feed ratio is 2-3.5. The equilibrium nitrogen conversion of circa 27 and the equilibrium ammonia concentration of 300 mol/m3 are obtained for ammonia synthesis at the optimum operating conditions of around 660K and 23 MPa. The average percent error for nitrogen equilibrium conversion and ammonia equilibrium molar flow is only 6.154 and 5.932 respectively compared to published data 22. © 2016 Published by Elsevier Ltd.