The pulsejet engine has always attracted the attention of researchers in the field of air-breathing propulsion due to its simple structure, low weight, and inexpensive manufacturing process. In this study, a parametric optimization was performed on an augmentor installed at the exhaust of a pulsejet engine. To this end, a transient axisymmetric numerical simulation of a valved pulsejet engine under flight conditions was carried out using ANSYS Fluent. The k–ω SST turbulence model was employed to capture the flow behavior, and the combustion process was modeled as a volumetric energy source. A suitable downstream section of the engine was selected to accurately compute the net thrust using the momentum equation. Simulations were conducted over multiple consecutive cycles until the flow and performance parameters exhibited harmonic oscillations. The thrust was then time-averaged over the final three cycles. Subsequently, assuming a cylindrical augmentor and parameterizing its geometry, the effects of three key parameters including the augmentor’s distance from the engine exit, its diameter and its length, on the thrust augmentation were investigated. Finally, a detailed aerodynamic analysis of the engine, with and without the augmentor, was presented. The results demonstrated that the optimized augmentor, by entraining ambient air and enhancing the exhaust momentum, increased the net thrust by approximately 170% compared to the configuration without an augmentor.