In this paper, MTDATA is selected as the electron donor and BPhen as the acceptor. The trianiline structure of the donor molecule provides a variety of charge transfer pathways for charge separation. Based on Marcus theory, the photoinduced charge transfer properties of non-fullerene acceptor organic solar cells (NFA-OSCs) in external electric field (Fext) were studied. By analyzing the changes of reorganization energy (λ), Gibbs free energy (ΔG), electron transfer integral (Vda) and charge transfer rate under the influence of Fext, it was found that Fext can effectively regulate the charge transfer. Moreover, the change of charge transfer rate under Fext is similar to Vda, indicating that Vda is the main factor affecting charge transfer rate. To a certain extent, this study provides theoretical support for improving the photoelectric performance of NFA-OSCs.