The electron trajectory equation of electrostatic wide beam has been researched thoroughly. Equations of curvilinear paraxial trajectories with second order approximation have been derived

and converted into a suitable form for computing. The computational rationality and credibility of curvilinear trajectories are demonstrated by concentric spherical system. There is a difference about fifth order of magnitude between firstand second-order approximate values of curvilinear trajectories

and about fourth order of magnitude between these two aberrations. It can be neglected in general engineering applications

but cannot be neglected in some image tubes requiring high precision.