In this research, industrial secondary reformer reactor has been modeled and simulated. In order to create a reactor design model for the secondary reformer in the ammonia plant.The first objective of the thesis is to study the effect of operation conditions such as feed compositions,pressure and temperature on the mole fraction of the product components, temperature and pressure of the secondary reformer. The effect of chemical reactions number in a catalyst zone has been investigated and two models have been studied. Also, the effect of catalyst shape and characteristics has been investigated where five types of a catalyst were examined under the same operation conditions. The experimental part deals with the evaluation the performance of secondary reformer relative to different operation efficiencies of ammonia plant (100,70 nd 65) % through study the effect of different molar flowrates of air. The results of the mathematical model have checked successfully against the data available in the manual and data daily log sheet of the reactor.The results depicted high accuracy between Simulation results and Plant data of the State Company of Fertilizers South Region in Basra/Iraq.