Fuel-air mixing is one of the challenging issues in supersonic velocities that is mostly used in scramjet engine combustors. Sufficient mixing between the supersonic airstream and the fuel jet is critical for designing of scramjet engines, and this is due to the very short residence timescale for the mixture in supersonic flows. Various studies and investigations have been conducted on enhancing the fuel-air mixture. One way to improve fuel-air mixture is to employ step before the injection point, so a low-speed recirculation zone is created before the injection point and causes to improve fuel-air mixture. Employing step causes to increase stagnation pressure loss and we should compromise between mixing efficiency and stagnation pressure loss. In this paper, the effects of step on Gaseous sonic transverse injection in supersonic crossflow are investigated numerically. Two-dimensional Reynolds Averaged Navier-Stokes equations and k-ω sst turbulence model and the perfect gas equation have been solved, using Fluent software. The results of the numerical solution are compared and validated with available experimental data. Numerical results showed good agreement with the experimental values. Then, the effects of varying step heights and distance of step from injection point on Mach disc height and stagnation pressure loss are considered numerically.