The present study is focused on impingement of underexpanded jet on a plane wall. Numerical simulations are carried out for various jet standoff distances (z/D) and Nozzle pressure ratios (NPR). The objective is to investigate the effect of NPR and z/D ratio on jet behavior, and formation of shock cells. Pressure variation on the target wall is also discussed. Results are presented in terms of flow parameters, viz. Mach number, pressure, temperature, and density. It is found that the distance from the impingement wall affects the shock cell formation, which in turn governs the pressure exerted on the wall. At higher NPR, Mach disc formation is also observed, and the change in flow field and wall pressure is discussed.