The effects of Coulomb interaction on the stimulated scattering by relativistic electron beams are investigated. The analytical expression for reflected laser field is obtained in the case of monoenergetic electron beam. It is shown that the contributing factor characteristic of Coulomb interaction is proportional to the square of electron density. If the electron density is relatively high and the incident radiation intensity is relatively low, the contribution of Coulomb force will be significant and its effects cannot be neglected.