The influence of plug shape on the performance of an aerospike nozzle thrust force is studied in different back pressure conditions. To generate smooth plug contours, Cubic B-Spline technique is employed. In the current research, basis functions are obtained using Deboor’ s relation. The flow field around the aerospike nozzle is investigated implementing various shapes, and the best of the generated configurations is determined. The flow field is simulated using Navier-Stokes equations and k-ε turbulence model. A triangle unstructured grid is applied for discretization of the governing equations. The computational methodology utilizes steady state density-based formulation, and a finite volume cell centered scheme is used to discretize the flow field equations. The flow field is divided into several zones to accelerate the solution convergence, , and an appropriate initial condition is assigned to each zone. Six different shapes of the plug are generated, and the effect of the spike shape on the formation of the shock and expansion waves is investigated in each case. The thrust force is calculated for each case, and the best configuration is determined in terms of the maximum thrust generation. Eventually, the temperature distribution is calculated along the nozzle for further investigations, and it is concluded that the best configurations show a lower temperature rise compared to other designs.