Abstract: A generalized theory of wide electron beam focusing with curvilinear optical axis on both the orthogonal and the non - orthogonal curvilinear localcoordinate bases has been studied by using the variational principle , in which theelectrostatic potential and the magnetic induction vector B in the laboratorycoordinate system are assumed to be known . The present paper represents a step further from the study of narrow electron beam focusing to that of wide electron beam focusing using the variational principle , and fully verifies the concordance between the variational method and the electrodynamic method in studying electron beam focusing .