4-Decyl-1-hexadecyl side chin is introduced into (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo [1,2-b: 4,5-b']difuran-2,6(3H,7H)-dione(IBDF) with the material 4-Decyl-1-hexadecyl bromide and 6-bromoindoline-2,3-dione, and then Stille couple with (E)-1,2-bis(tributylstannyl)ethene to obtain a poly-mer semiconductor PIBDFV-26 with large fused ring based on isoindigo (IID). The property, structure and morphology of PIBDFV-26 are characterized by TGA, DSC, UV, CV, XRD and ATM. The results show that the semiconductor PIBDFV-26 has good solubility in trichloroethylene (TCE) and good thermal stability. The HOMO/LUMO energy level is -5.66 eV/-4.62 eV and the optical gap is 1.34 eV. XRD results show that the polymer chains are likely packed in a lamellar crystalline structure with an edge-on orientation and the d-spacing and π-π stacking distance are 2.55×10-6 mm and 3.46 ×10-7 mm, respectively. AFM shows that the surface of the annealed PIBDFV-26 film contains nano-crystalline particles. The PIBDFV-26 is assembled into an organic thin film transistor (OTFT) device and tested, and the results show that the OTFT device ex-hibits n-type charge transfer characteristic. The average electron mobility of the polymer film annealed at 150oC is 0.13 cm2/V∙s.