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When a long focal area-array CCD camera takes photos in a TDI mode for dynamic lateral multi-frame imaging, it will output images with large size defect on the edge of image because of the high line transfer frequency or long exposure time and will influence image interpretation. To overcome the problems, the operating principle of area-array CCD in the TDI mode was analyzed, and the analysis indicates that the large size defect in the image comes from the invalid TDI transfer stages of the CCD during shutter exposure process. The obtained results were verified by a experiment and a method that the TDI transfer was finished simultaneously with shutter exposure was proposed to remove the invalid TDI transfer. On the basis of the analysis, a photo-electricity positioning synchronized was proposed and a photo-electricity synchronizer was developed to settle the headache. The results show that the image defect area is less than 15 column-pixels, which successfully solves the image defect from the area-array CCD camera in the TDI mode and improves its image interpretation accuracy.