In the present paper

computation of electrostatic field distribution for conical immersion lenses is studied by using the boundary element method（BEM）

and the electron trajectories incident from the object and image spaces have been traced using a set of curvilinear paraxial trajectory equations and practical trajectory equations

then the electron optical paramenters

such as cardinal points of lens

have been determined. The computational results coincide with the analytical asymptotical method given by S. Ya. Yavor et al.