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Conjugated polymers with nearly coplanar backbones have been the most commonly investigated materials for organic solar cells.Tuning the electron-withdrawing ability and molecular structure(planarity)in(donor unit)D-A(acceptor unit)conjugated polymers allows for design new polymers with enhanced electrical,optical and photovoltaic properties.[1] In this paper,the donor polymer PBDTDTBT(P0)was investigated by means of the density function theory(DFT)and the time-dependent DFT at the PBE0/6-311(d,p)level.The calculated results are in agreement with the available experimental data of the HOMO energy level and band gap.Then we further designed and studied nine new D-A copolymers(P1-P9)by substituting 2,1,3-benzothiadiazole(BT)unit in P0[2] with nine acceptor units,respectively.The DFT and TD-DFT calculations at the PBE0/6-311(d,p)level on the dimer models were also used to investigate the polymers of P1-P9.The calculations show that the copolymers(P3,P5 and P9)as promising donor copolymers for high-efficiency organic bulk heterojunction solar cells exhibit lower band gaps,stronger absorption and better charge transfer properties than P0.