We have synthesized a new conjugated polymer PBDTDT containing 4,8-dioctyloxybenzo[1,2-b;3,4-b']di-thiophene and 2,2'-dithiophene via a Stille coupling reaction. The copolymer was characterized by FTIR, NMR, GPC, TGA, DSC, UV-vis absorption, and electrochemical cyclic voltammetry. TGA showed that the copolymer exhibited good thermal stability. The optical, electrochemical, photovoltaic properties, and hole mobility of the copolymer were investigated and discussed. As a result, the polymer solar cell based on PBDTDT with a conventional device configuration of ITO/PEDOT:PSS/PBDTDT:PC61BM/LiF/Al showed a power conversion efficiency of 1.19 %, with a short-circuit current density (J (sc)) of 4.72 mA/cm(2), an open-circuit voltage (V (oc)) of 0.6 V and a fill factor of 53.3 % under the AM 1.5G illumination with an intensity of 100 mW/cm(2) from a solar simulator.