The authors concerns some relations between the field size and dose distribution of electron beams. The doses of electron beams are measured by either an ion chamber with an electrometer or by film for dosimetry. We anlayzes quailtatively some relations ; the energy of incident electron beams and depths of maximum dose, field sizes of electron beams and depth of maximum dose, field size and scatter factor , electron energy and scatter factor, collimator sharp and scatter factor, electron energy and surface dose, field size and surface dose, field size and central axis depth dose, and field size and practical range. He meets with some results, They are that the field size of electron beam has influence on the depth of maximum dose, scatter factor, surface dose and central axis depth dose , scatter factor depends on the field size and energy of electron beam , and the shape of the collimato , and the depth of maximum dose and the surfaces dose depend on the energy of electron beam, but the practical range of electron beam is independent of field size.