Abstarct: Abstract One of the effective parameters of a successful launch and missile hitting an object is to attain the operating pressure of a rocket motor. It is realized that the size of the nozzle throat and its variations (owing to the erosion as a result of burning the propellant grain which produces the combustion gases) plays a vital role in this respect. The current research focuses on the evaluation of the erosion rate in the nozzle throat due to variations in the propellant components as well as to utilize an energetic propellant. The method of propellant grain burn-back is numerically employed to determine the erosion rate in the Nitramine and non-Nitramine propellants; the results are then compared with the experimental outcomes. If 12% of the Solid explosive such as HMX is added to the composite solid propellant, the erosion rate of the throat area is almost decreased 25%.