The invention discloses a photon-number distinguishable detection-based true random number generator and belongs to the class of quantum secure communication. Different photon-number incident events are combined into a 2-bit random number sequence according to the uncertainty principle of poisson distribution by using the characteristics of a photon-number distinguishable detector capable of distinguishing incident photon numbers. The true random number generator mainly comprises a photon-number distinguishable detection module, a photon-number identifying and processing module and a random number acquisition module and can generate high-speed random secret keys needed in the quantum secure communication. The true random number generator has stable and reliable random sources; the generated true random number cannot be repeated or deciphered by the random characteristics of light quanta; a complex post-processing procedure is not needed; and the true random number generator is convenient to use.