Fiber is the fastest growing industries, and applications not only in communication but also has been widely used in other industries .For the future development of science and technology research worth exploring. The major work of this thesis is the introduction is optical mode of fiber, and then discuss the various features of the fiber and its scope is used to make the fiber can be accurately work in any position. The first chapter is an introduction. The second chapter we introduced the principle of optical fiber. The third chapter describes the most simple parallel waveguides using Maxwell's equations to derive various properties of the waveguide, and then understand TE mode and TM mode. The fourth, fifth and sixth chapters derive the basic fibers, understand their mode field solution, cut off conditions, and finally discuss fiber dispersion.