Abstract: The envelope correlation algorithm is the most widely used in range alignment of ISAR motion compensation.But the operation of traditional algorithm is very time-consuming.In order to speed up the operation and improve efficiency,this paper modifies the algorithm by firstly intercepting the major part of the echo profile,which represents the dominating scattering from target,and then performing envelope correlation operation.We also apply interpolation and spatial variant apadozition(SVA) technique to further improve the alignment accuracy.The computer simulation proves the feasibility of the method.