This paper presents a multi-retardation model for the complex birefringent phenomenon of an optically heterogeneous fiber reinforced composits. A multi-retar-dator matrix, and dedued from which，a group of light intensity, azimuth and retardator formula are given. Secondly, a equivalent theorem of the multi-retardators to two-retardadors is proved, which in turn leads to a point that the later should be considered as a kind of statistic equivalence of the former. The multi-retardator model can be explained briefly as follows. After having passed accross the heterogeneous medium, the emerging polarized light is of complex wave front and can be divided into a set of plane waves with different spatial frequencies, each of them being composed of a pair of orthogonal polarized rays. The coherence of all these waves at any point of any front screen prependicular to the original incident beam can be represented mathematically by the addition of their Jones vectors. Therefore, a multi-retard ator matrix resulting from the addition of Jones matrixes which are corresponding to each pairs of orthogonal polarized beam with different spatial frequency is used to characterize the birefringent behaviors of optically heterogeneous composites.