MAGIC and HESS’s detection of delayed VHE gamma-rays from Gamma-Ray Bursts (GRBs) has demonstrated the promising future of GRB afterglow studies with the Cherenkov Telescope Array (CTA). We have developed a model where we have explored the afterglow parameter space to see the detectability of sub-TeV photons by CTA. The spectral energy distribution is computed using a one-zone electron synchrotron and a synchrotron self-Compton model at a given redshift. We find that jets with high kinetic energy decelerating into a dense ambient medium are better candidates for CTA. In this paper, we have applied our model to fit the spectrum of a long GRB detected by MAGIC. The result indicates that our model can well fit EBL attenuated MAGIC afterglow spectrum.