The effects of re-scattering on the supra-thermal electron (STE) produced in moderate laser fields are analytically considered (laser intensity I is up to 5.0 × 101s W. cm-2) with a simple model. The electron kinetic energy distribution given by the model is consistent to that given by the particle-in-cell simulation. Based on this fact, it is shown that the scattering of electron in intenselassr by the ion in plasma plays an important role in the generation of STE in a moderate laser field.