High resolution pulse shaping based on the frequency comb has been widely used in microwave photonics, spectroscopy and communication optics and so on. To describe and evaluate the resolution capability of such a pulse shaping system, the ray tracing method is adopted to analyze the spatial dispersions of four schemes like single grating, parallel gratings, single grating with focus and anti-parallel gratings with focus. The spot spacings and sizes of different wavelengths can be determined from the modeling. As indicated by the calculation results, the latter two structures are advantageous to achieve high resolution pulse shaping; frequency combs with long wavelength, large mode spacing and big spot size are favorable for space dispersion; high grating groove density, small incident angle and multi passes in the dispersion system are conducible to the achievement of high resolution. The criterion for resolution would bring on some spot overlap noise.