Optical fibers are being studied more and more extensively in information and communication. Mode recognition technologies in optical fibers provide a concise method for fiber mode recognition. Transverse electric wave (TE) modes, transverse magnetic wave (TM) modes and mixed wave (HE, EH) modes are classified according to the scalar solutions of the fluctuation equations in step index fibers. Moreover, simulation studies are performed for representative optical fibers such as multi-clad Bragg fibers and photonic crystal fibers. And a universal mode classification method is proposed by combining the electric field line distribution of the mode and the electric field intensity distribution in the Ez direction, which helps researchers to do further investigations on optical fibers.