The performance of the aerospike nozzles is influenced by many factors. To identify how much influence each factor work on the performance loss, the major factors were analyzed, including the boundary layer losses, the chemical kinetic losses, the truncated losses and the base losses, as well as the losses inherent to the design. The model of the pressure distribution on plug wall was established according to the altitude compensation capability of the plug nozzle. The results show that the truncated losses and the base losses due to the truncation of the plug are the main factors influencing the performance of the aerospike nozzle. To reduce the losses and improve the performance , the gas flow features on the spike and base should be emphatically investigated by the experiments and the numerical simulations, and these features should be taken into account in the process of the aerospike nozzle design.