Sub-pixel positioning technology for CCD images is proposed to improve the astronomical location precision of space targets.The main factors affecting the positioning accuracy of targe centroids, such as image noise, discrete sampling error and window size selection are analyzed. Combining with the CCD imaging characteristics for dispersion spots, a location method for target centroids based on energy accumulation is proposed. This method uses the interpolation technique to reduce the illumination inconsistency between actual sensitive area and discrete sample points, and uses the energy accumulation of dispersion spot to select the efficient target window for optimizing target gray and eliminating random noises. Finally, a squared weighted centroid localization method is taken to calculate the centroid position. Experimental results show that the method has strong anti-interference ability and stability.It can offer a positioning accuracy of 0.01 pixel and is suitable for a low SNR condition.