A self-calibrating weak light detection device, comprising: a housing, wherein the housing comprises a reference compartment, a front compartment and a detection compartment communicating with the front compartment; a signal optical system, wherein the signal optical system comprises a signal light collector and a photon counting module, wherein the signal light collector and the photon counting module are arranged in sequence along an emission direction of signal light, the signal light collector is arranged in the front compartment, and the photon counting module is arranged in the detection compartment; and a reference optical system configured for calibrating the signal optical system, wherein the reference optical system comprises a diffuse reflection cavity, a reference light source arranged in the diffuse reflection cavity, a photoelectric detector, a photoelectric control panel electrically connected with the reference light source and the photoelectric detector, and a diaphragm making the signal optical system communicated with the diffuse reflection cavity, wherein the photoelectric control panel is electrically connected with the photon counting module; the diffuse reflection cavity, the reference light source, the photoelectric detector and the photoelectric control panel are mounted in the reference compartment, the diaphragm makes the signal optical system communicated with the reference compartment, and light of the reference light source enters the signal optical system through the diaphragm after being subjected to diffuse reflection in the diffuse reflection cavity, and is projected to the photon counting module, wherein the diffuse reflection cavity is a cylindrical cavity, wherein the diffuse reflection cavity is provided therein with a light blocking device and a light passing channel, so that direct light of the reference light source is shielded from entering the diaphragm and light of the reference light source enters the diaphragm through the light passing channel; and the reference light source is mounted on an inner surface of a side wall of the diffuse reflection cavity, the side wall is disposed on the photoelectric control panel and the photoelectric detector is mounted on the photoelectric control panel at a mounting height lower than that of the reference light source relative to the photoelectric control panel so that after light emitted by the reference light source is diffusely reflected in the diffuse reflection cavity, a part of light is detected by the photoelectric detector. a housing, wherein the housing comprises a reference compartment, a front compartment and a detection compartment communicating with the front compartment; a signal optical system, wherein the signal optical system comprises a signal light collector and a photon counting module, wherein the signal light collector and the photon counting module are arranged in sequence along an emission direction of signal light, the signal light collector is arranged in the front compartment, and the photon counting module is arranged in the detection compartment; and a reference optical system configured for calibrating the signal optical system, wherein the reference optical system comprises a diffuse reflection cavity, a reference light source arranged in the diffuse reflection cavity, a photoelectric detector, a photoelectric control panel electrically connected with the reference light source and the photoelectric detector, and a diaphragm making the signal optical system communicated with the diffuse reflection cavity, wherein the photoelectric control panel is electrically connected with the photon counting module; the diffuse reflection cavity, the reference light source, the photoelectric detector and the photoelectric control panel are mounted in the reference compartment, the diaphragm makes the signal optical system communicated with the reference compartment, and light of the reference light source enters the signal optical system through the diaphragm after being subjected to diffuse reflection in the diffuse reflection cavity, and is projected to the photon counting module, wherein the diffuse reflection cavity is a cylindrical cavity, wherein the diffuse reflection cavity is provided therein with a light blocking device and a light passing channel, so that direct light of the reference light source is shielded from entering the diaphragm and light of the reference light source enters the diaphragm through the light passing channel; and the reference light source is mounted on an inner surface of a side wall of the diffuse reflection cavity, the side wall is disposed on the photoelectric control panel and the photoelectric detector is mounted on the photoelectric control panel at a mounting height lower than that of the reference light source relative to the photoelectric control panel so that after light emitted by the reference light source is diffusely reflected in the diffuse reflection cavity, a part of light is detected by the photoelectric detector.