Abstract: This paper describes the aberration and distortion of e-beam deflection magnetic field in which the parameters keep close to in the normal solution. The relationship between the principal trajectory of e-beam and aberrations has been investigated in combined round magnetic lenses and deflection system of SDS-3 e-beam machine．Formulae for the first-order chromatic and third-order geometrical aberration coefficients of superimposed magnetic focus and deflection field of both electric and magnetic type in the case of a point source on the Z-axis are obtained．The aberration of superimposed focus-deflection system is so small that the dynamic correction is unnecessary.