In this article the mechanism of spreading of optical radiation in a Bragg fiber is considered. A mathematical model for analysis of a Bragg fiber viewed as a flat multilayered dielectric structure has been proposed. The method of geometrical optics of description of spreading the light is used. Formulas connecting the clad refractive index with fiber parameters are given. The light attenuation at its refraction in the multilayered clad and chromatic dispersion are calculated, as well as the dielectric loss of the clad material. The dispersion and the width of the waveband of Bragg fibers with different number of layers and low waveguide modes have been compared. Examples of fibers with different coefficient of dielectric material loss are included.