In this paper, P3HT∶PTB7∶PC ₆₁BM is used as an active layer to prepare a ternary heterojunction organic photodetector covering the visible light range. The effects of PTB7 added to P3HT∶PC ₆₁BM system on the optical and electrical properties of organic photodetectors (OPDs) are studied by atomic force microscopy, ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. It is found that when the mass ratio of P3HT∶PTB7∶PC ₆₁BM is 8∶2∶10, the response spectrum of the ternary mixed layer extends to 780 nm, and the responsivity (R) of OPDs reaches 178, 291, and 241 mA/W respectively under 630, 530, and 460 nm light and –1 V bias, and the specific detection rate ( D*) reaches 10 ¹²Jones, and the above results are compared with the research group’s previous results about P3HT∶PBDT-TT-C∶PC ₆₁BM as the active layer of ternary organic photodetector. The phenomenon of the device performance gap caused by adding two polymers PTB7 and PBDT-TT-C based on benzo[1, 2-b∶4, 5-b]dithiophene (BDT) units into the same system P3HT∶PC ₆₁BM is analyzed. The effect of PTB7 on the micro-morphology of the mixed film due to the introduction of fluorine atoms and the reason for the increase in the mobility of photogenerated carriers in the film are explained. This OPD with better preparation performance provides a theoretical basis and method.