The effects of the location of the cavity behind the pylon on the supersonic combustion of the ethylene jet were studied numerically. Free-stream flight condition of Mach number 5 at an altitude of 25 km was considered, and the isolator inlet conditions were obtained using two-dimensional inlet simulation. The equivalence ratio of 0.15 was considered for this study. The position of the cavity behind the pylon was varied from 0 to 60 mm with a spacing of 20 mm. A steady Reynolds-Averaged Navier-Stokes equation set with species transport was used in this study. The SST K- \(\omega \) turbulence model was taken as the closure model. The validation of the equation set was performed using experimental data from the literature. The simulation results indicate that the position of the cavity behind the pylon plays a vital role in combustion characteristics. The pylon and cavity with 0 mm separation and floor injection produced a normal shock train due to thermal choking, and the direct interaction of the cavity with the incoming boundary layer. The cavity with 20 mm separation showed better penetration and less spreading in the lateral direction compared to the 40 and 60 mm separation cases. The combustion efficiency and total temperature were higher for the 0 mm separation case, but the total pressure loss was also higher for the 0 mm separation case than the other cases. The total temperature rise of 300 K was achieved for the 0 mm case, whereas 150 K was achieved for the other cases towards the exit of the domain. A total pressure loss of almost 35% was observed for the 0 mm separation case. The 20 mm separation case showed the lowest total pressure loss among all the cases.