The moving patterns of space targets include both flying straight and rotation around the axis，it requires linear motion compensation in ISAIL imaging process.The target flight speed used in the compensation process can be measured by heterodyne receiver mode.This method is accurate and fast，it is more accurate than the speed estimating method used in the past.The principle of space target heterodyne velocity measurement，motion compensation and reconstruction imaging are presented.The effect of speed estimation method and heterodyne velocity measurement method are simulated and compared by MATLAB.The superiority of heterodyne velocity measurement method is confirmed，such as higher imaging resolution，less information processing，faster computing speed and so on.