Abstract: Aerospike nozzle engines are considered as a candidate for the next generation of propulsion system for reusable launch vehicles because of the possibility of improving performance.In order to provide an insight into performance and to control flow field development of plug nozzles,numerical optimization of truncated plug nozzles was performed by solving the Navier Stokes equations.Parameters investigated included spike length,pitch angle and secondary flow rate.Results indicated that significant performance gains result from the external freestream expansion,which self adapts to external pressure variation,as well as the short compact design for high expansion ratios.The expansion waves,compression shocks and the separated base flow dominate the flow structures and affect the aerospike nozzle rocket engine performance.Secondary flow may eliminate the recirculating base flow region and better performance will be obtained.