An amorphous-silicon photoelectric device and a fabricating method thereof are disclosed. The amorphous-silicon photoelectric device includes: a substrate; a thin-film transistor and a photosensor with the photodiode structure, which are provided at different positions on the substrate; and a contact layer; in which the contact layer is located below the photosensor, and the contact layer is partially covered by the photosensor, moreover, the contact layer and the gate-electrode layer in the thin-film transistor are provided in a same layer and of a same material. According to the technical solutions of the present disclosure, the fabricating procedure of an a-Si photoelectric device can be simplified, thereby improving the fabrication efficiency and reducing costs.