Compensation of dose distribution of an electron beam for the oblique incidence is to shift the standard isodose curves according to the distance of the air space. The error of the corrected distribution from the measured one was more than 10% when the space was more than 2 cm in 8∼12 MeV electron beam. The electron beam diverged approximately in accordance with the inverse-square law when the scattering foil was assumed to be the virtual source. Correction of the air space shifting and the inverse square law resulted in an error less than 3%.