The cut-off process of optical stopping effect in thin film waveguide with doping As2S8 and pure As2S8 is studied. Based on this, the chemical bond structures of the samples are analyzed. With the help of the theory of hybridize valence orbital and the theory of electron energy band gap, the dynamical equation of optical stopping effect is proposed. The numerical analysis results are well agreable with the experimental data, and the cut-off process of optical stopping effect can be explained by the deduction of this model. It reveals the mechanism of cut-off process of optical stopping effect.