In this article, the aberration theory of the combined electromagnetic focussing cathode lenses is described, and the two previous representative papers concerning the aberration theory of cathode lenses, the first contributed by Ximen Jiye (1957) and next by B. B. Bonschtedt (1964), are emphatically analyzed and commented. It is shown that the formulae of aberration coefficients for the cathode lenses given by them, although different in form, can be transformed from one to another; and it is enough to prove that the criticism of B. E. Bonschtedt addressed to Ximen Jiye, is improper.It is worth noicing that the aberrations of cathode lenses must be considered atthe image plane with regard to ε(x1)-a certain initial energy of electron in axialdirection, then the formulae of all the transverse aberrations including the first order and third order aberrations for the combined electromagnetic focussing cathode lenses can be derived. It is expected that these formulae will be closer to practice than those derived formerly.