Optimization of the ammonia synthesis unit to increase ammonia production is studied in this line of research. In this paper, the steady-state ammonia synthesis is simulated using Aspen HysysV.11 software, by comparing the simulation results with industrial information, a mean relative error of 7.71% was obtained, which indicates the high accuracy of the simulation. Then, four effective variables were selected from 11 independent variables by the Plackett-Burman method. The effects of the Hydrogen flow in the feed stream, the Recycle stream pressure, Feed stream temperature, and Input third reactor temperature were simulated, and the response surface design method of central composite design was performed to optimize. It is obtained that the Hydrogen flow in the feed stream is equal to 6255 kmol/hr, feed stream pressure was equal to 205 bar, the temperature of excess stream inlet in the first reactor was equal to 663 K, and the temperature of stream inlet the second reactor to 677.5 K which increased to 7.5% ammonia production.