Abstract: Effects of electron beam parameters, including radius, emittance and energy, on bremsstrahlung exposure angular-distributions at a distance of one meter in front of the target, are discussed in this paper. The fit formula for beam radius and emittance is obtained in order to get the maximum forward exposure. The higher the beam energy and the less the emittance, the better the distribution of exposure. The positions and angle spreads of all beamlets are calculated with both analytic and Monte-Carlo methods. The results are in agreement with each other.