To measure the sub-pixel image motion of the sequence images which are captured by the high-speed camera at the high frame rate with poor SNR, the joint transform correlator (JTC) is used. The relative image motion of the two adjacent images can be measured by inputting these images into the correlator. The principle of this method is described, and the effect of the defocussing of the CCD in the JTC on the accuracy is analyzed. To research the measurement performance of the JTC concretely, the experiment platform is set up. By using different images with different image motion, the results showed that, the JTC can measure the sub-pixel image motion entirely even for the images with SNR=1, and the measurement error submits to the normal distribution, which implies zero mean and the RMS is no more than 0.12 pixel under the conspicuous level is equal to 0.05.