To measure the sub-pixel image motion which is caused by satellite attitude instability or vibration, the optical joint transform correlator (JTC) is used, which is based on using the auxiliary plane CCD to record the image motion in the focal plane of the satellite camera. The principle of this method is described, and the experimental platform is built. The measurement performance of the JTC is researched. The results show that the JTC can measure the sub-pixel image motion of the space camera entirely, and the accuracy is not variable with the contents of the input images. The measurement error submits the normal distribution with the mean of zero, and the root mean square (RMS) error is no more than 0.12 pixel under the conspicuous level of 0.05. This can meet the operating requirement of the space camera completely.