Abstract: Based on the framework of the tight binding approach, the formation of an exciton in inter-coupled polymer chains is studied. Both a localized exciton in one single chain and a spread exciton between chains are obtained. It is found that an excited electron-hole pair is more inclined to evolve into a localized exciton. By analyzing the effect of the interchain couplings on the exciton binding energy, it is shown that the photoluminescence efficiency of the polymer in a dilute solution state is higher than that in a solid state.