A series of donor-acceptor copolymers composed of benzo[1,2-b:4,5-b ]dithiophene (BDT) as donor and other conjugated monomers as acceptors were designed and synthesized for applications of polymer solar cells (PSCs).We performed DFT calculations on their monomers and found that their HOMO-LUMO energy level could be modulated by using different side chains on BDT or adding new blocks.We also performed molecular mechanism calculations to obtain the planarity of copolymers.The results of theoretical calculations are in good agreement with the experimental results.