Supersonic combustion is a transformative technology for next-generation hypersonic propulsion systems, enabling efficient and sustained flight at extreme speeds. However, achieving stable combustion in supersonic flows remains a critical challenge. The primary goal of our study is to investigate the influence of backward-facing step (BFS) heights on combustion and mixing performance in a strut-equipped supersonic jet combustor. We have conducted our computational simulations using the 2-D Reynolds-averaged Navier–Stokes (RANS) equations to examine step heights of 2, 4, and 6 mm. The realizable k–ε turbulence model was utilized for analyzing the turbulent flow. The simulation results were first validated against available experimental data, confirming the reliability and accuracy of the simulation approach. The results demonstrate that BFS height significantly affects the size, strength, and stability of recirculation zones, which is a significant factor in fuel-air mixing and flame anchoring. The 4 mm step height emerged as the optimal configuration, striking a balance between enhanced recirculation and minimal flow losses. It exhibited superior mixing performance, uniform heat release, and robust flame-holding, as compared to the 2 and 6 mm configurations. The 2 mm step height showed inadequate recirculation, resulting in weak combustion, while the 6 mm height caused excessive separation and higher aerodynamic losses. These findings provide critical insights for optimizing supersonic combustion performance, contributing to advancements in aerospace technologies.