Using the modified effective Hamiltonian for non degenerate Raman process, we calculated the evolution of the atom inversion and studied the influence of AC Stark shift on the collapse revival phenomenon of Rabi oscillations. It is shown that in the presence of AC Stark shift, the atom inversion in non degenerate Raman process has a beatiful periodicity, and the frequency and amplitude of the Rabi oscillation are affected by AC Stark shift.