Abstract: The numerical simulations of the flow field around aerospike nozzle were completed based on N S equations with second order NND scheme.The attention is paid to the effect of the base bleed on aerospike nozzle at sea level,middle and high altitude.The results indicate that both the quantity of bleed mass flux and the magnitude of base pressure are the causes that induce the swirl in the base area to disappear.Though the bleed can enlarge the thrust of the aerospike nozzle,it lessens the specific impulse except the case that the bleed is small at low flight altitude for the linear aerospike nozzle.