Absolute calibration method and system for photon number

The invention discloses a photon number absolute calibration method and system. The method comprises the following steps: measuring the photon number A of a single laser pulse emitted by a laser by using an energy meter; the laser emits a laser pulse to enter the atmosphere, and the laser pulse is scattered by the atmosphere and then enters a telescope in the telescope array to be converted into a digital signal B; in sunny weather just after snowing or weather without snowing, the steps are repeated to obtain the absolute gain G of the telescope, and the proportion fi of the number of photons emitted by the laser to the number of photons arriving at the entrance of the telescope in the weather without snowing is obtained; repeating the steps for other telescopes of the telescope array to obtain the proportion of the number of photons emitted by the laser to the number of photons arriving at the inlets of all the telescopes; solving the attenuation proportion g1 of the atmosphere to photons through the propor