This paper is the second part of a theory of the coherent propagation of light wave in semiconductors. After considering the interaction between electrons, the problem of a semiconductor interacting with light is discussed and the equation of exciton polarization wave excited by light wave is obtained. We point out that the equation can be approximated by a set of linear ones and the exciton polarization wave can be regarded as a Bose field only in the limit of low excitation. In this paper, the problem of coherent excitation of discrete exciton level is also discussed specifically. It is shown that the discrete exciton level system excited coherently is approximately equivalent to a two-level atom system excited by light wave in which the difference of energy level is dependent on the degree of excitation and the density of equivalent "two-level atoms" is determined by features of the exciton state wave function.