Considering that the quantum key distribution protocol may be affected by the detector dead time in practical applications when the photon transmission rate is too high, the relationship between the security key generation rate based on the heralded single photon source protocol and the detector dead time is explored. First, the relationship between the security key generation rate and the detector dead time is explored with or without considering the detector dead time. The results show that when the photon transmission rate is too high, the dead time of the detector will indeed affect the generation rate of security key. Then the security key generation rate is further analyzed under different detector dead time. The results show that for the same lightsource, the greater the detector dead time is, the smaller the security key generation rate is, and the relation between the limit value of the security key generation rate and the detector dead time τ is 4.2/τ.