The invention discloses a perylene tetracarboxylic diimide copolymer containing a dithieno quinoxaline unit as well as a preparation method and application thereof. The copolymer is shown in the specification. The preparation method comprises adding a perylene tetracarboxylic diimide dibromide and a 6,9-bis(tributyl tin)-dithieno[3,2-f:2',3'-h]quinoxaline derivative in an organic solvent, adding a catalyst, carrying out Stille coupling reaction at the temperature of 50-120 DEG C for 24-72 hours, and refining to obtain the copolymer. The copolymer disclosed by the invention can be applied to manufacture of polymer solar cell devices, organic field effect transistors, organic electroluminescent devices, organic light storage devices, organic nonlinear materials or organic laser devices. Thecopolymer disclosed by the invention has the advantages of good solubility, strong light absorbency and excellent charge transfer performance, the absorption range of the copolymer can extend to a near infrared region, and the sunlight utilization rate can be increased; and the preparation method has a simple synthesis route and a low process requirement.