The invention discloses an all-fiber photoelectric detector with ultrahigh sensitivity based on a composite structure comprising fiber end face coupling graphite and organic perovskite nanometer crystal (CsPbBr3). The detector is characterized in that a pair of metal electrodes are plated on the side wall and the end face of a fiber. The metal electrode of the side wall is connected with the metal electrode of the end face; and a composite structure formed by a graphite thin film and an organic perovskite nanometer crystal covers a channel region between the surface of the metal electrode of the end face of the fiber and the electrode. According to the invention, new ideas of preparing a photoelectric conductive layer and a contact electrode on the end face of the fiber and achieving an all-fiber photoelectric detector with ultrahigh sensitivity are provided; through the prepared fiber detection, functions of light transmission and weak light signal detection can be achieved; any discrete optical element is not required; the detection and the preparation method have wide application prospects in communication and sensing field; and the preparation method is simple and high in yield.