In order to calibrate the number of photons contained in the unknown pulse, the signal difference of the system output was measured when the light pulses with different photon numbers were under microwave kinetic inductance detector (MKID) effect in the superconducting environment. The average interval method and iterative method were adopted, and the theoretical analysis and experimental verification were carried out. The results show that, the number of photons of unknown 1550nm single-pulse light in the cryogenic measurement system can be identified by MKID. After data processing, the average photon numbers were 1.98 and 1.81 respectively. Among them, the process of calibrating the number of photons by the average interval method is relatively simple, and the iterative method needs to be further explored. It is helpful for single-pulse photon number detection.