The rapid development of optical communication and optical sensor technology is raising new requirements on the performance of optical fiber,which caused the introduction of many optical fibers with new index of refraction. As one of the new type optical fiber,Bragg fiber has many advantages that can hardly be reached by ordinary optical fibers. For more comprehensive analysis of Bragg fiber,it took ordinary stratified fiber coax as the example for the introduction to the basic idea of transfer matrix method first. The idea was then used in the mode calculations for Bragg fiber,then limited clad fiber Bragg model was analyzed as the degradation of the situation of infinite cladding. The design principles of the Bragg fiber were studied further.