Abstract: Fiber-based photodetectors are expected to be widely used in the field of wearable electronics due to their properties of flexibility, easy-to-weave, and omnidirectional light detection. Currently reported fiber-based photodetectors mostly use inorganic photosensitive materials, which have drawbacks such as limited mechanical flexibility and complex preparation processes. In this paper, we proposed the fiber-based organic photodetector (FOPD). The electron transport layer (ZnO), organic heterojunction photosensitive layer (PBDB-T:ITIC-Th), and hole transport layer (PEDOT: PSS) were prepared on zinc wire by a solution dip-coating method layer by layer. Finally, silver wire or carbon nanotube fiber (CNT) was wrapped as the external electrode, and two kinds of flexible FOPDs were obtained and showed typical rectification characteristics. They showed a specific detection rate of 10¹¹ Jones (300 nm~760 nm) at −0.5 V bias. Due to the better interface contact between the CNT external electrode and photosensitive layer, the CNT-based device exhibited lower dark current density (9.5×10⁻⁸ A cm⁻², −0.5 V) and faster response speed (rise time of 0.88 ms and fall time of 6.00 ms). The work is expected to provide new ideas for the development of flexible fiber-based devices and wearable electronics.