Abstract: Hydrogen dissociation in the process of electron assisted chemicalvap or deposition（EACVD）of diamond thin films is simulated by using Monte Carlomethod. The model of hydrogen dissociation through electron impacting is suggested . The energy distribution of electrons and H atoms on the surface of the substra te are obtained. The results are of great importance to the study of diamond thi n films deposited by EACVD.