Based on the description of the charge transfer process of a time delay integration charge coupled device (TDI CCD), it is pointed out that the relative displacement of the target image and the transferred charge introduces the charge transfer image shift problem in a line transfer period, which leads to the decrease of the modulation transfer function (MTF) in the scanning direction. Based on the basic definition of MTF, the charge transfer image shift model of the TDI CCD is established. According to the quantitative calculation of this model, the MTF curves of the three-phase TDI CCD are obtained under the condition of different pulse widths of computer interface (CI) signals. The MTF changes with the pulse width of CI signals, and the maximum value at the spatial Nyquist frequency is obtained when the CI signals are equally spaced, which is difficult to achieve in the actual system because of the limitation of computed radiography readout signals. In this paper, we present the improved TDI CCD driving timing, which makes it possible to realize the equal interval distribution of CI signals by adjusting the technology compatibility kit signal. Finally, the experimental platform is built, and the MTF curves are calculated from the obtained target images. The result is consistent with the theoretical model.