Scattering effect has great effect on machining morphology in sapphire processed by ultrashort pulse laser. On one hand, scattering leads to saturation of machining length despite the increase of pulse energy. On the other hand, scattering results in undamaged core in the elliptical damaged shell. When the laser intensity is above half the damage threshold, the electric field is scattered to 0 and doesn’t contribute to the laser intensity at latter position. The physical model which combines scattering effect, linear and nonlinear optical effects matches well with machining morphology of sapphire at different laser parameters, including pulse energies, focus positions, focal length and pulse duration. At first laser with lower pulse energy, for instance 25 μJ, processes the inner part of sapphire. During micromachining of sapphire, the focus positions move from the bottom to the top. At last the laser with higher pulse energy, 150 μJ for example, fabricates the surface. The objective lens with the focal length of 20 mm is suitable for machining sapphire and the optimal pulse duration is 950 fs.