In this paper, the one-dimensional band structures of poly (para-phenylene) (PPP) and its alkoxyl derivatives are calculated by an extended Hückel method (BICON-CEDiT code). The results of the band gaps Eg of these materials are in agreement with the available experimental data. In addition, we found the band gaps of PPP's alkoxyl derivatives become wider as the carbon atoms increase in alkoxyl side chain. The calculation indicates that the heteroatom and side groups have an obvious effect on the band structure of polymer, which is also consistent with the experimental results. The results are useful for synthesizing PPP with different emitting wavelength.