Interaction of cosmological gamma-ray burst radiation with the dense interstellar medium of host galaxy is researched. Gas dynamical motion of interstellar medium driven by gamma-ray burst is investigated in 2D approximation for different initial density distributions of host galaxy matter and different total energy of gamma-ray burst. The maximum velocity of motion of interstellar medium is 1.8x104 km/s. Light curves of gamma-ray burst afterglow are calculated for set of non-homogeneous density, gamma ray burst total energy, and different viewing angles. Spectra of gamma-ray burst afterglow are modeled taking into account conversion of hard photons (soft X-ray, hard UV) to soft UV and optics photons.